a/v software well it personal preference realy, this question has been asked b4 and u wont get a diffinitive answer cos everybody uses something different.
i personally use kaspersky a/v on xp workstns and bitdefender on my server. i also every now and then use a free trial version of what ever is about to do a check on what i normally run, just as a check (as none of them ever find all nasties, over the years have used norton/macaffee/sophos )
kaspersky seems to feature in most survays/tests done by comp mags etc and does very well, very good level of protection and real easy to use.
you will also find the same level of disagreement with firewalls too but u didnt ask about that..........
some use xp firewall........i think its been improved with sp2, as i said b4 u wil get many recomendations for firewall, its what u are comfortable with, some like 2 controls (on/off) others like millions of things to tweek.....
i use a dedicated linux pc running smoothwall (possibly overkill but hay i want to be safe)
what ever u use it is worth going to some check sites