It doesn't really matter that much anyway, any decent 3d card should handle the realtime 3d requirements of Premiere 1.5 or 2.0. At least, that's been my experience, I use premiere alot... a decent X1600 or 7600 GS should do fine.
Meh, I can list some major Nvidia screwups, too. (Grotesque GeforceFX era optimizations, anyone? Or even todays texture shimmering at default settings...)
But the fact is for video editing, it doesn't matter. Ati drivers are great, and so are Nvidias.
In fact, if you're into video rendering and encoding, Ati's AVIVO drivers will give you a huge speed boost in some circumstances. Purevideo doesn't yet use the GPU to accelerate encoding, from what I understand.
depends on what kind of acceleration, and if the software makes use of the hardware... MPEG-1 ecompression is ancient, MPEG2 at least is accelerated by geforce3 and more recent, but MPEG4 is a bit more dodgy - and doing video editing in WMV is tantamount to committing suicide, due to lax sync, destructive compression algorithms and uneditable format.
OK - nice, however not many people/hardware use H264 yet (MPEG4 is h.263). But, if you have the opportunity - and your editing software actually knows how to use this acceleration, then by all means use H264 and avivo.