Be sure you have installed the Detonator 6.31 drivers ... other versions are not meant for a VIA chipset. Remove all traces of the previous drivers before installing the card.
Other possibilities:
1.) Heat. I had to install three fans to cool my GeForce2 GTS card. One blowing directly on the card, a slot fan right underneath the AGP port, and I replaced the old heatsink/fan combination with a Blue Orb. Then I took the old heatsink, cut it up, and put the pieces on the memory chips. That made a big difference. If you try this, be sure use a good thermal compound, like Arctic Silver.
2.) Memory Bandwidth. I had real problems with lockups while playing DVD's and running games until I overclocked the memory on the card. GeForce2 GTS cards have a fairly bad memory bottleneck, and raising the memory speed does wonders. You can get instructions for the Registry hack for these cards, (and how to overclock the card) at:
<A HREF="http://www2.anandtech.com/showdoc.html?i=1246&p=5" target="_new">http://www2.anandtech.com/showdoc.html?i=1246&p=5</A>
I raised the memory clock to 393MHz, and this caused the stuttering and lockups to disappear.
Finally ... I made some changes in the BIOS. I changed the AGP Aperture Port to 128, enabled Fast-Writes for the memory, (Fast R-W Turn Around), and enabled both the AGP Master 1 WS Write and AGP Master 1 WS Read.
Then I overclocked the whole system. I didn't get far, because of the multiplier lock on the processor, and because the VIA chipset doesn't "like" a Front Side Bus over 105. (I'm currently running 1000Mhz@1030.) But this was enough to make the system act like it had been given a tune up, like a car ... and it's been rock solid ever since.
To those of you who might wonder why I didn't mess around with the L1 bridges ... I have a MicroStar mainboard, and have no way to adjust the multiples in the BIOS without affecting the FSB and the PCI Bus, so I left the bridges alone. Not everyone has an ASUS board. Unfortunately.
This worked for me. It should work for you guys, too.
Not only is my system stable, it's fairly fast. I can play any game I wish, without problems ... and I managed to get a decent 3D Mark score of 7463 at 1024x768x16.
I did update my BIOS to version 1.6, and added a hardware mpeg card for playing DVD's.
I hope this information proves to be helpful.
...Toejam31