> It's the commercial where there are a whole bunch of people dancing, but you see them one at a time, and they're actually silhouettes... Whats the song that plays?!

There are currently 3 iPod Silhouette TV ads with the following music:
Vertigo by U2
Walkie Talkie Man by Steriogram
“Saturday Night” by Ozomatli

Hope that helps. All ads can be viewed at
http://www.apple.com/ipod/ads/

Enjoy!