No, you won't be wiping your drive... at least not if you have upgrade media. You will be performing a clean install which will back up all of your User folders as well as your Programs Files folders to a folder called Windows.old. If you have anything in any other folders, then it would be a very good idea to back it up... it's a good idea to back up EVERYTHING for that matter... things can and do go wrong after all.
 
I just had a look and it turns out all my other folders were intact as well... the only folders that get touched are Users, Program Files, Program Files (x86) and Windows. Still a clean install, but without a format.

I know a straight answer is always nice, but it's not always possible. There are always caveats.... especially when it comes to Windows.