open a console and do
yum search "software that you want"
then if it finds anything
yum install "software name"
that'll search the redhat repositories for software, they don't have as many as the 3rd party ones like fresh rpm , dag, lavina etc. and also nothing like MP3 cause of licensing, google for adding freshrpm to your repositories and adding it's key.
FC3 repositories also only have fedora specific RPM's (obviously) and so they're very easy to install (yum handles all dependencies too) however some things may not be available for it and in which case you'll need to hit their website for source etc.
then you can get even more software, i use xmms for music, once you add freshrpm you can search yum for "xmms-mp3" for mp3 support, mplayer is good for movies, you can do similar to above for different codecs (might be .wma codecs).
Anti-virus is really not needed, antivirus is only good on linux for scanning windows shares and emails AFAIK.
If you want to just browse types of software and see what takes your fancy sourceforge is brilliant (although if you want to look at EVERYTHING it'll take a while)
Before looking for loads of new stuff to get i'd go through and see what you already have from the install CD's (evenign starting it up and checking the "about" in help may provide useful info) you might find alot of stuff you want is already present
Google is your friend