Um, am I allowed to go back on-topic? Hello? I don't wanna break the Cellar rules, I'm not here very often.
I recommend you boot Vista just far enough to burn a set of recovery disks, if it didn't come with any. No need to do a backup. And if you already have those, you can skip Vista completely.
MS "upgrade" disks usually let you install clean, as long as you can prove you have the previous version. I don't know how to do this with Win7; try booting the Win7 disk directly and see what options it gives you. You should be able to do it in a single session instead of the 2 or 3.
That's my instinct anyway.
This article seems to indicate it should be that simple, but
that article says maybe not.