Process involved in planning a surprise party for a 17 year old (when party requires nothing larger than a sheet cake for servings):
1 - at DD's 16th b-day party mention to relatives that it would be fun to throw her a surprise party next year (since she doesn't appreciate the shin dig you provided for her 16th -- gotta one up it, ya' know!)
2 - 11 months later, send invites to DD's friends (e-mail family 'cause it's more convenient and doesn't require postage ... besides they'll get it quicker and since you put it off .... )
3 - Call a baker a week before the event (preferrably when you're waiting for paperwork for new car to be completed) 'cause the baker shouldn't need too much more time than that .. they're doing all the work the day of the party anyway, right?
4 - The day of the party, make sure your maid did a good job cleaning the house.
Then, run to party supply store and pick up plates, napkins, plasticware and some hellium balloons. If you're really good, throw in some streamers to add stress to your day! On the way home, stop off at grocery for soda pop and ice cream.
I mean really, how hard is it to plan a party for 20+/- people?????
I'm with you dawncr -- make the girl feel like the party/cake was the surprise (SOL, kid, but I hope you like what we did get you). The car should have been the surprise ... the rest of it she won't be focusing on. Of course, now she's saying "Thanks for the car daddy, but I wanted it in _____ (insert color here). And, where's my cake?"