I have a X1950 Pro AGP and until now there was no way to get 3D and XVideo working.
Configuration files were correct but trying to play a video with "xv" acceleration always get a black screen.
Same thing with 3D, for example starting glxgears popped up a black screen. The program was running (it showed me FPS) but that was all.
Tried with games too. I was able to hear sound but no images.
Then on a thread on this forum (sorry, don't remember who wrote it) I read about a phantom hidden menu in BIOS for setting AGP aperture, (in my BIOS there was no way to change aperture size, it was fixed to 128).
Setting aperture to 256 solved all my problems
So here is what I did:
I have an AWARD bios version 6.00PG.
Enter the BIOS pressing Canc during boot and in main menu press CTRL+F1
Enter in Advanced Chipset Features and TADA!, you'll find "AGP Aperture Size (MB)".
Hope this can help.