how exactly did you update your drivers? uninstalled first I presume?
what Video card do you have?

Hum, I dont know much about newer norton's from what I hear its working great
anti-virus programs shouldnt make 3DGS perform poorly, if so, it's blocking 3DGS, or its scanning while you are using it.

Please list what system you got
RAM
256 and 512 mb on windows xp tends to perform less and less after the updates, atleast, that was what I noticed.
Video card
Perhaps the drivers dont work correctly with this card if its "outdated"
Cpu
if it's viruses it can be effected alot if its a old one because small amount of processing power compared to new ones.
Motherboard
as some motherboards tend to get poor in performance if its a really budget motherboard