Good luck. And don't expect that you can do the same type of "upgrade" that is supported from Vista. I just had occasion to reinstall Windows 7 using the "custom" method referenced in
Dwight Silerman's original blog entry on the subject. It's true that this type of upgrade will allow you to install Windows 7 into an existing partition and file system, and that it does take the old installation and rename it into a folder called "Windows.old". But it does NOT pay any attention to the old installation at all - it is in fact a brand new installation into an existing file system.
What this means is that any customizations, software installations, user accounts etc. that were present in the original system are NOT in the system you just installed. While the previous software is still sitting in the "Program Files" folder, it is not integrated into the Registry, start menus, etc. So you're basically starting over from square one just as you would if you installed the non-upgrade version.