Vista is basically just an upgrade to Windows XP and didn't really do anything besides slow certain systems down.
Go to
Gizmo's Freeware Review page and download and try what is the recommended FREE application for your needs.
No reason to pay for anything to do what you want done.
If you want to start over from scratch, format your drive but not just by 'formatting'...use
Darik's Boot and Nuke to completely wipe your drive clean.
Also, you should have a Microsoft label somewhere on the computer case that has the registration key. Using that key may allow for you to install a new copy of the 'exact same' operating system.
Or, you could find someone that could send you a legal copy of Windows 7 and you could just install that.
-Tim