Stuff like antivirus and Firewall software is always monitoring stuff, so takes resources away from anything else you're doing, so benchmarks will generally improve slightly without them.
I would simply say that if your system is stable, and you're happy with the <i>actual</i> gaming performance, then why bother tweaking?
It's easy to get too concerned over benchmark scores, but you didn't build the thing just to run benchies on did you? :lol:
Apart from have your drivers up-to-date and tweaked properly, and ensuring you're not wasting resources by running background apps that you don't need, the only other way to improve performance would be overclocking, But I wouldn't suggest that to a newbie-esque Prescott owner, unless it's winter and your heating's not working
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Epox 8RDA+ V1.1 w/ Custom NB HS
XP1700+ @200x10 (~2Ghz), 1.4 Vcore
2x256Mb Corsair PC3200LL/1x512Mb Corsair XMS PC4000 2.5-3-3-7
Sapphire 9800Pro (VGA Silencer Rev3) @418/742