I remember reading some article about dressing sexy for a Halloween office party a couple of month ago. The paper said - don't do it, even though it's a party and not work and it's a nice chance to meet people you work with in a less formal situation, the next day at work, everyone will still remember what went on in the party, and people might be effected by the memories to change their mind about you in office situations.
The whole office party issue is confusing - on one end it's a party, on the other it's office, it feels a little bit like a contradiction in term.
My suggestion, dress cooler then you would at work, like push on colors and style, but don't go too sexy or too wild. try to think of what you want your co-workers (and boss) to think about you and dress to match that impression.
Also, don't get drunk or anything like that, it's good to have fun, it's good to loosen up in moderation, but what goes on in office parties, doesn't always stay in office parties...