Win 7 was supposed to back up windows XP so we can go back to XP
There is no direct upgrade path from XP to 7. You would have to do a clean install of windows 7, therefore there is no way to "uninstall" windows 7 to get back to XP. Whoever told you you could back out to XP was wrong. If you did a custom install, windows 7 will have backed up your old windows folder by renaming it to windows.old, but that's just so you can access those files, not to uninstall from.