I got given a license of 8 ultra which exhibited the same skippiness. I tried those beta drivers out last night, but they gave me no improvement, which is expected imo as the 8800gts doesn't hardware accelerate h264 decoding as far as I recall.
Either way though... TMT3 still working nicely. Sat down last night and watched the first half of the film in full HD. Was excellent quality and silky smooth. Shame PowerDVD is still having these issues on my machine.