Hey, I recently came across this same issue on my Evga Nvidia 6200 AGP which gave me, Code 12, 640x480 4 bit color, conflicting with VGASave and all that other BS. I placed in a call into Nvidia and after an hour or so they tell me to RMA It. I knew this wasn't going to be an option since I didn't want to wait.
So I start playing with bios settings. Everyone is saying its the onboard video, My bios doesn't allow me to disable it. Which is due to the fact it's supposed to auto disable in a VGA device is detected. Well anyways, straight to my SOLUTION, I had my AGP aperture size set to 256, and I was thinking this is a 512 card, but it won't let me raise it up to 512... WTF... So I then come across this page stating...
"AGP Aperture memory will not be used until your video card's on-board memory is running low. That means it will usually not impact your gaming performance because developers are trying hard to not exceed the on-board memory limits.
The bigger your video memory, the smaller your Aperture Size could be. However with later games requiring more and more texture memory a good number seems to be 128MB Aperture Size for all cards with 64 MB to 256 MB Video RAM.
Setting the Aperture Size to HUGE values will not increase performance because this merely sets the maximum amount of physical memory that can be used. It only makes the GART Table bigger because every 4K page has its own entry, no matter if allocated or not.
Setting the Aperture Size to too small values could result in running out of available texture memory especially on a low-mem video card. It is also possible that developers make use of the GART's features by creating textures as 'non-local'.
If you experience in-game stuttering try playing with the size of your Aperture."
So I lower my AGP aperture size (in your Bios which is usually accessed by pressing the F2 or Delete button at your Motherboards info screen at the very start of the boot sequence.) to 128 and viola! So if you have this issue try lowering your aperture size and see if that helps. Not sure if it will be your solution, but I haven't seen anyone past this from all the threads I went through. A pain in the butt, but better than an RMA. I also called up Nvidia and told them they should consider adding that to their trouble shooting documents they read from since most of them just read and don't know what they are talking about. Anyways, hopefully this will help someone. Even if it's just 1 person, I know I would have liked to of seen all the solutions available.