OK. For the P3, you could download something like CentOS, it is stable, and includes programs for everything. version 4.1 comes on a DVD. It is a rebuild of RHEL so you know it is a good product.
For yours, I wouldn't worry about the viruses. Just know which files to watch for, in other words, don't email your friend a Windows executable you downloaded from a porn email
. (jk of course). I have yet to email a friend a virus from my Linux computer, with no antivirus protection.