I've done this briefly with my PowerMac 8500 back
around 1997, which was
where I came up with the idea. The 8500 has the advantage of being able to
handle both NTSC and PAL signals (not sure what other Mac's succh as yours
can handle).
The 6500 also did NTSC and PAL. Apple really only made one video input
setup, they just packaged it onto different cards for the different
machines.
Actually, I used to use my 6500 to convert PAL videos to NTSC. I used a
PAL VCR to feed the signal into the PowerMac, then played the video in
full screen mode, and connected its NTSC output to another VCR. It worked
quite well actually, and had the nice side effect of bypassing
macrovision as well (the 6500 acted as a TBC since its NTSC output wasn't
really outputting the source video, but rather an image of the computer
desktop that just happened to have the source video playing in full
screen).
-chris
<http://www.mythtech.net>