Vista uses the same file system as XP, so there isn't that much of a dropoff due to incompatibilities. The important thing, though is to stop using that computer. The more you use it, even during the recovery process, the greater the chance of you overwriting the data and never being able to recover. Connect the hard drive to another computer as a secondary hard drive and run the file recovery software from that system. To get you started, the top three user-ranked recovery applications compatible with Windows Vista are Easy Undelete, GetDataBack, and Data Scavenger.

Best of luck.