Well I decided to try it out and see. I imported the HD/MPEG-4 video into WMM 6 on my brothers Vista PC. It worked? why was everyone telling me it wouldn't?

Anyway, I can edit it fine and all that. But trying to get it to Play in in the preview screen on WMM (so I can find parts I want to edit/delete and where to add titles etc) isn't good. It plays really slow, judders, starts, stops and so on. Is this because of the PC spec? Do you need a relatively high spec PC to be able to play/edit HD videos?

I can play the video absolutely fine in Quick Time, runs smoothly, just how it should. When I play it in Windows Media Player, it plays the same as in WMM, slow, judders and starts and stops.