Motherboard and Gaming

I have a Asus P5GD1, I built my own pc and i use it mainly for gaming, now i have intel pent 4 , lga775 prescott and it was running alittle over 60c idle so i go tthe xp-90c and now my temps dont get higher then 28c, but other then that, i still get gitterness when i play source or any game and the video card i have is a nvidia gefore6600 not a gt, some people say that its my video card then i should upgrade to ati and im thinking about purchasing the x850 but on the other hand, Could the gitterness be from my motherboard cause i mean myt temps for my mobo have decreased greatly as well since i installed the xp-90c, to idle at about 30c and on load about no higher then 32c, so my mobo is always cool, im just curious and worried that if i get this x850 it bight bottleneck or somethin im just a very worried person when it comes to stuff like this cause its like if i buy and i still get the gitterness what is there to blame next. Ive evenm checked if my ram is puttin in the amount it should and it is, checked processor how much of its putting out , its all good. so what is there next to blame..

Comp Specs:

Intel Pent 4 [2.8 ghz]
160 gb hd
1 gig ram
geforce 6600
480 Watt Power Supply

One thing is for sure, that 6600 non-gt on source engine games is gonna struggle unless you take your settings waaay down. Source engine games were designed with and for ATI cards so if that's all you play then yeah, you'll want to get an ATI card. The X850XT/PE are excellent cards for sources games. I have one and can play HL2 and CS:Source on max settings and 1280x1024 res.

I hope that helps a little.