I ran Nod32 with windows XP and it was great. No noticeable slowdown with operation. That was years ago though. These days i install Microsoft Security Essentials. It's free and seems to work. To be fair though i don't stray to far from the light in terms of the websites i visit. My sister has managed to circumvent MSE and get her computer infected multiple times.
Avid Stamp Collector - I really love 39 Cent Stamps