Up until the Nvidia N40 came out in april 2004, no graphics card did anything for editing where you en/decode movies, it was all ram and cpu, the gpu only let you see what your doing so it not matter if its the slowest or faster card in world, but n40 claimed to have a PvP (called PureVideo) which lowers cpu usage taking work to the gpu to en/decode certain movie codecs, the agp 6800U is broken for all but mpeg2 and the 6600 and 6200 does work and i think all the pci-e card work, the new 7800GTX probably works for all.
Inverse telecine (3:2 pulldown)
Motion adaptive deinterlacing (SPAD)
Color space conversion
Gamma correction
Processor amplifier
WMV9/H.264 motion compensation
WMV9/H.264 in-loop deblocking
Noise reduction
Frame rate conversion
MPEG 2 Decode / Encode (SD and HD resolutions)
MPEG 4 Decode / Encode
DiVX Decode / Encode
High Quality scaling
The above was what Nvidia site claimed the AGP 6800U would do at launch and they later edited it to be far less, but i saved page on day 01 of launch.