What to worry? The anti-virus protection from your ISP is probably just fine. The most basic protection is in how you use your computer. Avoid opening strange attachments, downloading from strange sources (such as Limewire, etc), and stay away from **** sites.
The truth is that all anti-virus publishers will circulate updated protection and definitions once a new virus gets into circulation. Some may do it faster than others.
Personally, I use AVG free as my installed anti-virus protection. I back it with the free online scans from TrendMicro and eTrust. Both of those onlines will remove problems, not just identify. If I'm really not sure, I'll try other onlines that will just identify.
A piece of software that should be installed is MOVE ON BOOT. This will help get rid of nasties that are being exectued.
Oh yeah, I also use Spybot and SpywareBlaster.