Studio 12 (and even 11) wer written from the start to run on Vista, whereas 10 was modified after it was written. Studio 11/12 should be more trouble free under Vista.
What makes 12 better? Depends what sort of editing you do, really. Probably best to watch the What's new in S12 videos on the Pinnacle website. if you just do SD, but like complex effects, then you might find the montage feature useful. You can now rotate videos with a rotate and advanced 2D plug-in
Welcome to the forum, Jake