<< I am not aware of any special DVD features on the Geforce (still), so it's basically the same as using just your CPU for watching DVD. There are a few reviews that did a comparison with the DVD playback too, just look around. >>
There are two hardware accerated features in the GF2/3, three in ATI and 4 in the 'GF4'. Note these featuers are not DVD specific, but can be used for any video playback (however often aren't).
A Hollywood+ card or clone is 100% DVD decoder, your computer basicaly provides the card with a data steam, but if you don't want a dedicated card, ATI probably has the best DVD decoding. There is one point though, new CPUs are more than grunty enough so they don't need ANY hardware acceleration.