AFAIK, the MPEG card is used only for decoding MPEG-1. All other formats are handled in software by QT. As a result, you can find a situation where your Mac plays the more complex MPEG1 with grace, but chokes on Cinepak, for example.
The MPEG card is great for allowing stutter-free playback of VCDs. I'd love to figure out a way to shoehorn that into a Color Classic (properly modded with a motherboard that accommodates such a thing, of course), but that's for another day...
As for the most modern version of QT that's 8.1-compatible, that's QT5.x. It'll work with 7.5.5 through 9.2.2.
The MPEG card is great for allowing stutter-free playback of VCDs. I'd love to figure out a way to shoehorn that into a Color Classic (properly modded with a motherboard that accommodates such a thing, of course), but that's for another day...
As for the most modern version of QT that's 8.1-compatible, that's QT5.x. It'll work with 7.5.5 through 9.2.2.