"my G3 has hardware-based DVD playback which 10.1 doesn't support."
Ummm, Yes it does. I have both played and burned DVD's on my 733 from X.
Or do you mean that your video card Does the decompression?
Apparently according to this article, MacOS X still doesn't support DVD playback on my B&W G3: http://docs.info.apple.com/article.html?artnum=106470
I've been told that the newer Mac that are supported for DVD playback ahve software based DVD decoders whereas the older machines have Hardware based decoders.