whoops, forgot about Apple TV. That's an excellent option. The question would be which version.
The prime advantage of ATV is that you have an onscreen interface AT your party or in your living room, rather than choosing a playlist on your computer.
I have the "Old" Apple TV which I LOVE. ( _
http://www.amazon.com/Apple-TV-160GB-Hard-Drive/dp/B000RQHAUA/ref=sr1_2?s=electronics&ie=UTF8&qid=1289178072&sr=1-2 ) $149 at Amazon.
It's big compared to the new one but has a full complement of outputs (HDMI, component, optical, RCA). More importantly, it has a hard drive, so you can transfer your music & vids to the ATV's HD. You can ALSO stream directly from your computer, but I believe it's slower than the new model. Personally I prefer having the hard drive, so I don't need to be using the computer just to stream. BUT bear in mind there will be no further software updates for this model
The latest Apple TV one is cheaper ($99), streams music and video. It's teeny, doesn't run hot, But only has HDMI. My only concern is that it is SO new. You may want to check these forums to make sure that all is working well. It has some additional capabilities (I think including Netflix - but I'm not sure, so check it out if you're interested.
Good luck, seems you have several options to confuse now...