Sorry I only saw this now that you've done it. Hope it works out. I would have urged you to Upgrade the Vista, because of this post that's been up for months on Technet from a Win7 Team member's blog:
Harold Wong's Blog Site : Can I do an In-Place upgrade from Windows 7 Release Candidate To Release Code??
Would be interesting to hear back from you on how it works out, as others want to do this.