Did you know that it's impossible not to backing-up and lose your old files during Windows 7 installation? That's right! Microsoft contradicting it-self in the first steps of installation preparation step by step information.
At first they say that we should back-up our old files as they WILL BE deleted.
Then they practically force an option of where our old Windows files will be backed up into Windows.old folder.
So the folders such as "Users, Program Files, Windows ...etc" will be stored in Windows.old folder.
And any other files created by you that are stored in "C:\" directory will remain untouched!
So don't worry about upgrading or backing up anything, since Windows 7 does it all for you!
My advice, just go with a clean install and you'll be safer that way. Now back to business...