What format are they in? If its WMV, then the only way is to get a very old ver of Virtualdub and use that, since the old ones had WMV support. Although if you want to fiddle the framerate, you'll probably be best advised to output a high wuality thing from that, and then re-encode the AVI for GP with a newer one.
You could also try a .wmv --> AVI converter; there are a few around - but a lot of those output shoddy vids.
If they're real, then the only way I can think of is to use Virtualdub's videocapture feature (which I don't understand, so don't ask) on a player playing the video in question - possibly using the RealAlternative codecs, since they work in most players...