cjl :
Intel quad. Q9450 is a good choice.
So is a $100 AMD 6000+ dual core.
I run 4 security programs (one is PG2 blocking 1,169,125,052 IP #'s in my custom list) while running 10 torrent files -and- playing Frontlines:Fule of War at the same time.
2 GB of RAM and a 2GB page file with XP Home and only using 46% of the -physical- RAM.
See my forum profile for my older (3 years) systems (7) that I run on my game LAN...50% OC on air and stock volts.
MB and PSU matter as well.
If you want to go Intel the E8400 is a good CPU yet still overpriced for what it does in real life vrs other options.
Z