To clarify what exactly did you do?
Did you just delete the old partition, or did you delete it, create a new one, and reformatted the new one?
If it is the later your chances are pretty slim.. even if you did not reformat it your odds are still very slim because the newly created partition would have destroyed some structures that are originally in the old one. If you merely just pressed 'L' when in Windows XP setup, and at that very point in time you get that sickening feeling in your gut about what you've done (and being a clever user you quickly turn off your PC) you have good chance of recovery.