Doesn't need a clean install really. Also Flexnet (formerly known as installshield) allows you to download an evaluation version of their adminstudio. I use that for years now and it shows me every change a program makes. It's made for repackaging but I like to use it to capture registry settings and file changes as well.
Have you tried it on Vista yet? I've tried a couple registry monitoring tools on Vista and they choked and did not provide full/accurate details.
