The "hurtling sideways down a dirt road" type of rally is usually categorized as a performance rally. Because certain expensive safety equipment is required by the rules (primarily a roll cage, fire suits and helmets), and certain expensive modifications are strongly advised (such as rally tires and uprated suspension), entering a performance rally is not very accessible to a novice of modest financial means.
A road rally is basically free of cost by comparison. Road rallies are held on open public roadways at speeds that are (at least on average) below the posted speed limit. Cars are usually unmodified "daily drivers," with only a few basic safety items required, such as a warning triangle and a first aid kit.
The basic gist of a road rally is that you're given a set of directions incorporating average speeds, along with landmarks, times, and/or distances at which to change your average speed. The goal is to arrive at a set of checkpoints (whose location is generally kept secret) at the correct time.
The way a road rally is set up is that the organizer (or "rallymaster") chooses a route, usually on a scenic or otherwise interesting road. He or she then chooses a reasonable average speed for each section (always below the speed limit if the rally takes place on public roads), and picks out landmarks (quite often road signs) to designate where the average speed will change. The next step is to measure precisely the distance between the landmarks, and the location of the checkpoints. Finally, the time that the vehicles are to pass each checkpoint is derived from the distance and specified average speed. The rallymaster compiles a set of "route instructions" that specify the average speeds, landmarks, and directions.
The directions are written according to a very specific set of rules laid out in the "general instructions" which are usually available well in advance of the rally (e.g. on the organizer's Web site) and are quite often handed out together with the route instructions before the start of the rally.
The competitors in the rally need to stay on course and follow the average speed for each section, as well as change speeds at the landmarks. This would be relatively straightforward on a route with no curves or stops. To keep things interesting, these sorts of routes are usually avoided. Thus the competitors have to resort to various tricks -- and the occasional bit of "spirited driving" -- to keep up with the specified average speed.
Almost all road rallies are run with a driver and a co-driver, along with (somewhat rarely) any additional passengers. The co-driver's job is to read the route instructions and tell the driver where to go and how fast to drive. The driver and the navigator (another name for the co-driver) usually share responsibility for spotting the landmarks listed in the route instructions.
Technically-minded people will note that keeping track of the proper speed is made trivial if a precision odometer along with a reasonably accurate clock is mated to a computer in the car. Such "rally computers" are fairly common, but will place the competitors in a class with similarly-equipped cars.
Times, Speeds, and Distances
Times in road rallies are based on a hypothetical "Car Zero" (car numbers signify nothing more than the starting order). If the event starts at 6 PM, the first car leaves at 6:01 PM. Subsequent cars leave (in order of their number) at one minute intervals. When the route instructions list car zero as passing a point at, say, 19:23.20 (that's 12 seconds after 7:23 PM) and you are in car number 20, you need to leave that point at 7:43:12 PM.
Again, speeds are specified as averages (using the acronym CAST, meaning "change average speed to," even when there is no change involved). The CAST (it's also used as a noun) will be a few miles/kilometers per hour below the posted speed limit to allow you to slow down for curves, stop signs, and traffic lights and not have to exceed the speed limit to keep your average speed on track.
As mentioned earlier, the directions are described via a very specific set of rules. One instruction might be 'L onto Main St.' which is different from 'L at "Main St".' The first instruction tells you to turn left onto the street called Main Street and stay on it even if it changes direction later. The latter instruction tells you to turn left when you see a sign (as defined in the general instructions) that says "Main St" -- not "Main Street" -- onto an eligible road (also as defined in the general instructions). "Trap rallies" make a point of using such technicalities to trick the competitors into choosing the wrong direction, wrong speed or wrong time at which to change speeds.
Competitors are scored at locations called checkpoints. A checkpoint crew records the time at which the car arrives at or passes the checkpoint, either with or without the competitors' knowledge. (Do-it-yourself checkpoints also exist, where the competitors record the time they pass a specified landmark). Usually a point is given for every second or hundredth of a minute that the car arrives early or late. Usually a cap exists, such that you can't rack up more than, say, 300 points on any given checkpoint. The points from all the checkpoints are summed up, and the competitors with the lowest score wins.
Most events have a novice class, with neither the driver nor the co-driver having entered more than a certain number of events. Another common class is "S.O.P." (seat of pants), which restricts the equipment to be used to the vehicle's stock odometer, a pen and paper, and a basic watch or stopwatch. An "unlimited" or "equipped" class allows a computer (electronic or otherwise) to be connected to the car's wheels to measure distance (GPS units would probably also put you into this class).
As mentioned earlier, some rallies incorporate "traps" in the route instructions. These are commonly called TSD rallies. The term is somewhat interchangeable with a road rally, although the latter term connotes an absence of traps (sometimes called a "tour" rally).
Most small events take place on paved roads close to major urban centers. Larger events will often incorporate gravel or snow-covered roads, and will traverse greater distances in rural areas. Many large events take place over two or more days.
"Brisk" rallies have the average speeds set close to the legal speed limit (and often faster than a reasonable person might otherwise drive). A performance rally is little more than an infinitely brisk road rally (the allowed time for stage is zero), which understandably requires the course to be closed and the cars to be specially equipped.
Some rallies are known as gimmick rallies, where some "skill" other than driving at a given speed is tested. An example of this would be a rally incorporating a scavenger hunt.
The first step, assuming you have a car and a friend, is to find an event to enter. Events can be found in the US by visiting the Sports Car Club of America (SCCA) Web site, or in Canada through the Canadian Association of Rally Sport (CARS) site. I imagine most first-world countries have similar organizations, and countless local clubs who may or may not be affiliated with national and international organizations also hold road rally events.
Good introductory events usually last from 1 to 3 hours and usually cost between US$10 and $20 to enter. This covers the cost of insuring the event and miscellaneous expenses (such as printing up instructions) associated with organizing the event. You'll want to budget for a full tank of gas, and you may want to have some money left over for the usual post-rally restaurant meal. A good watch (I prefer digital), a pen, a clipboard and a reading light will make the event much more pleasant.
Plan to arrive at a short rally (such as one of the common "First Friday Nighter" rallies) with at least an hour to spare before the "First Car Out" time. You'll want to leave time to fill up with fuel, possibly grab a snack, register for the event, and read the general instructions. You'll also want to set your watch to official rally time.
Once you register, you'll receive a set of general instructions and a set of Route Instructions (although these are sometimes given out later, say at half an hour prior to the start). The general instructions describe the organizers' basic rules (such as which way to turn when the route instructions don't specify a direction), and define some acronyms and terms. The route instructions are specific to the event and describe in detail where and when to turn, change speeds and so on. You'll probably also receive a car number. You'll have to put the car number someplace visible and also remember it.
Your out time will be the "Car Zero" out time plus your car number in minutes. Then it is simply a matter of following the route instructions (with any ambiguities resolved in the general instructions) and attempting to stay on course and on time.