Feel's like a storm is brewing, I've gotten a few emails today from various security lists about the W32/Blaster worm. This worm effects Windows NT 4, 2000, 2003, and XP, here's the info from M$. Block ports 135, 139 and 445 (RPC DCOM) in your firewall.
By the way here are few security mailing lists you should be on if you run windows and or you have a computer connected to the internet: