Has this bug been fixed yet? I've been experiencing this issue for well over a year now, and it's quite unbearable to disable AGPgart support. Mpeg4 video playback (when in high resolutions) and 3d applications cause a ridiculous choke on my 2.8 GHz pentium 4 processor. This is a mythtv computer that I would rather not buy new hardware for. I don't think it's unreasonable to wish for mpeg-1/2 acceleration via the GPU while simultaneously being able to take advantage of the AGP bus. The overall experience has left me quite frustrated and upset with Nvidia and has made me reluctant to buy more cards from them. I'm not saying open your drivers, but if you're going to keep them closed, please make them work
I'm willing to provide any testing/debugging info for you. I'm not at home at the moment, but I will give you verbose Xorg messages with the debug flag set in my environment for XvMC. Please Nvidia, fix this problem.
I'm using an intel i865PE chipset using a Gigabyte 8IPE1000, although I can reproduce this problem using an Asus board with a similar chipset. I've used both the kernel's GART as well as Nvidia's. This is 7600 GT card, XvMC configured properly on both machines. Just to clarify, XvMC does work with NvAGP set to not using any AGPGART implementation, which causes unbearable bottlenecks for the graphics performance.