If you install vista on a partition with a copy of windows already, it puts your old installation in a C:\windows.old directory so that you don’t lose any of your data (my documents, desktop, etc).
Unfortunately, there was a problem with my re-install (late in the process). If I reinstall again, does anyone know if I’ll keep my original windows.old folder and just get a second one with the failed install, or will it overwrite my windows.old.
While I don’t know the answer to your question specifically I believe this site’s instructions should help you rename the windows.old folder so it definitely won’t be overwritten. Just follow the instructions through the “Rename the Windows and Program Files folders” section replacing “windows” with “windows.old” in step 3. After you have renamed the windows.old folder you can exit the repair console and reinstall Vista without fear of loosing your data.