Okybugs-- I have seen two different corporate antivirus schemes put to use that I have liked, Norton Corp AV which seems to always be the first company to find a solution and fix for the latest bugs

OR Sophos seems to be a good one at another company I have worked for. Either way I recommend if you want good protection there are a series of things you need to look into.

Protect the systems, Protect EMAIL we use Antigen as the First tier of protection for email followed by a program by broadware (I think is their name) It does a deep scan and allows more detailed blocking of extensions and spam mail. Both Sophos and Norton or XP compatible and I like the layout of Norton.