The firmware will need to be re-flashed to work on sprint's network. You'll need to find someone who will do this and more than often you will not be able to surf the web, calls will drop or not come through, and plus you will have to convince Sprint to activate the IMEI which they are pretty serious about not activating phones they do not support.
If there was a SPRINT droid they would be more willing to since it is supported.
Sorry, your out of luck.