Problems with 9600np

I just recently purchased a new system with a Sapphire Radeon 9600np and the performance is lacking.
I get this odd frame lag when I play 3d games even when I'm NOT playing online.
The frames almost seem to skip and I get this problem even when I'm running my resolution at a paltry 640x480.
I've tried comparable systems with a Gforce Ti4200 installed and it seems to blow mine out of the water.
I've tried all the latest Ati drivers and even the Omega drivers.

Here are my specs...

Asus AN78X mobo
xp2500+ Barton
Hynix pc3200 256mb x 2 (dual ddr config)
Sapphire Radeon 9600 Atlantis
Windows 2000

Help!

btw...

I'm running Cat 3.7 and DX9.b

I had the EXACT same problem as you. I figured "Ahh, **** it. I am gunna crank this baby and to her max."

So.. I cranked up the AF to it's max, set all it's performances to max in the drivers, and only left AA at 2. I went into the games I was having problems with and TADA! No more problems for some reason. Now I Was getting exquisite graphics and respectible fram rates.