Well, as far as there being 4 flavors of Vista, it depends on what you use it for. Vista is the same in every version, but there is extra software in the enhanced versions.
Vista Home – includes Media Center but not Remote Desktop or backup software
Vista Business – includes Remote Desktop and backup software, but not Media Center
Vista Ultimate – includes everything, including some extra software that you’ll never use
Microsoft claims that the VALUE of this extra software is worth the upgrade. Instead of buying a seperate backup solution, you get it with Ultimate, blah blah.
If you don’t need remote desktop, then Home is all you really need. If you do (like I do), then get Business or Ultimate. I have Ultimate just because I’m awesome, but if I had to PAY for it then I would have settled for Business.