What do these words mean?
The best definition of bioinformatics I've run across comes from UCLA's graduate program:
Bioinformatics is the study of the inherent structure of biological information and biological systems. It brings together the avalanche of systematic biological data (e.g. genomes) with the analytic theory and practical tools of mathematics and computer science.
Computational biology seems a bit harder to define. It stretches from modeling single molecules to creating computational neural networks that help researchers understand real networks of living nerve cells. Neither of these things are the same as evolutionary computing. However, all kinds of computational thinking can be applied to biological problems, such as can be seen at NASA's Evolutionary Cell Computing Project.
People get into this fusion of biology and software from different angles. Most often researchers have a background in biology and teach themselves the computer science and programming skills. Sometimes a person with experience with computers finds themselves working in biological applications. In the past few years degree programs have sprung into existence, but they vary in emphasis. Some stress computation, and some stress biology and biophysics. (A quick Google search will turn up programs from all over the world.) No matter how people come to the field, there seems to be demand for more.
What does this really mean in practical terms?
There are academic applications, corporate jobs, and even practical work for people who have an interest in computing and biology. The biggest problem for academics and biotechnology-based pharmaceutical companies lies in making sense of the wealth of genomic data. One big relational data problem has not been solved, which is how to correlate genetic data with biochemical data. Proteomics is the word replacing genomics as the hot new field.
If it seems esoteric and academic, there are medical applications. The data generated by gene chip experiments are provocative -- knowing what genes change in cancer or other disease states. Combining genomics with proteomics means that not only will there be diagnostics for disease, biomedical researchers may be able to develop a clue as to what the genes actually do. But these applications hang on finding a way to sift through and correlate information, to find patterns which might emerge from a wealth of data.
Computational biology also has impacts outside of medicine. An attempt to model a biological system, the sense of smell, led to the development of an artificial nose geared toward the detection of land mines. Essentially, it's an attempt to re-create a dog's nose. The Tufts artificial nose grew out of two biologists interested in olfaction. Computer models of nerve cell circuits in the salamander became the basis for the neural networks of an artificial chemosensing device.
That all sounds pretty esoteric
My prejudice is clearly academic. Bioinformatics and computational biology could be rich fields for someone interested in both what computers can do, and what can be done with computers.
For those of more practical mind, there are eleven job openings listed at Aventis Pharmaceuticals alone. Two hundred and eight US jobs show up on a quick monster.com search, admittedly ranging from sales rep to Ph.D.-level specialist, including software engineers and UNIX system administrators. The problems tend to be interesting, and the toys are often up-to-the-minute. There are database and relational database problems. There are pattern-finding computational problems. There could be a career you might not have considered before
Other Links of interest:
Human Genome project bioinformatics page
The Open Lab at bioinformatics.org