As others have said, you should use this as a learning experience about the importance of backups, particularly when doing anything risky like repartitioning the disk or installing a new OS.

That said, there's a chance that PhotoRec or a similar tool (there are some Windows-specific tools that are similar in broad strokes, but I don't have any URLs handy) may be able to recover some files. Be aware, though, that the longer you use the disk in its current state, the more likely it is that additional files will be irrecoverably damaged or erased. Thus, if you really need any files from that disk, STOP USING IT IMMEDIATELY! Use it only along with PhotoRec (or something similar), and be sure to use another physical disk as the recovery target.