Look at arduino tone library.
http://code.google.com/p/rogue-code/wiki/ToneLibraryDocumentation#Arduino_Core_Version
About MP3 shield i guess u were talking about this ?
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1259561121/0
I did some research, and found lots of little audio players
What if u emulate button presses with arduino?
It might have some delay but should work.