If you use linux, viruses should really not be too much of an issue. Depending on your distro, you're either going to be getting 99% of your binaries from trusted sources (package repositories) or by compiling them directly from the source. Second, as long as you're not running root all the time, a virus should not be a problem, as the only thing it can wipe out is your home directory (which you should be regularly backing up anyway).
That being said, I myself don't run any AV software myself, but the installation should be pretty self explanatory. Download the source, then follow the instructions given in the file INSTALL (thats what its usually called anyway).