I know MC3 is old but I now have a Winxp computer that I can use strictly a DAW--get rid of all the windows/internet stuff that slows things down.  I was running MC3 on Vista 64bit and it imported FLV files without a hitch.  Now that I've migrated back to Winxp, it gives me the "Unable to import . . . Unrecognized file format . . . format not supported. . ."
Any ideas?
 

That's not because of MC3, it's because you probably don't have an FLV codec on your WinXP machine.  you'll have to download a player or codec pack from a 3rd party provider to get it to work.
 
google:  flv codec
 
 

Thanks for the quick reply.  Downloaded an FLV player, checked the list of video codecs on my Vista machine--all were on the XP machine plus more--couldn't really figure it out.  The good news is, that going through all this I found my problem was not due to speed/latency.  I used my Keystudio 49i as the MIDI output instead of the on-board sound card on the Vista machine and it works fine.
Thanks again for the ideas.