It isn't uncommon for new pumpkin plants to droop considerably when they get in a new environment. When this happens don't get to discouraged. Take the pot inside (if it isn't planted yet) and give the plant a little water. Pumpkins can be a little finicky at first and when they get unhappy they will tell you very quickly. Just give them a little TLC and they usually come back around.
If you have any great tips for transplanting new plants please let me know. I'm always happy to get a great new tip.