I'm running Windows Vista RC1 Build 5600 64bit Edition, and Multimedia Fusion 2 is running perfectly without any glitches at all. It's up to date, and no compatibility mode was used.
Right after Multimedia Fusion 2 is started up, after installing updates and bonus packs:
At the frame editor after opening "Emerald Challenge":
The 'Create New Object' dialog:
Title screenshot of Emerald Challenge running:
Screenshot playing Emerald Challenge without any framerate issues.
The Multimedia Fusion 2 About dialog:
Windows Vista System dialog:
These screenshots come directly from installing Multimedia Fusion 2, installing the automatic update, and installing the bonus packs.
I'm not having any issues getting it to run, so perhaps you had a sour install, or you're using an older build of Windows Vista. Even then though, Multimedia Fusion 2 ran fine in Beta 2 for me.
Yeah I'll agree it's rather CPU consuming but it's better than iTunes now imo, and winamp is ok but ... well I can't really fault it to be honest! I just found it annoying to navigate around my library of 4000+ songs That's where WMP handles things better really.