I have a 2000 Grand Prix with a stock delco 1 CD radio and was wondering if anybody knows how to add an aux input for an mp3 player to it.

I've seen a couple sold modified like this on ebay, ex:

FACTORY REMANUFACTURED PONTIAC FIREBIRD 7 EQ CD RADIO - !! MP3 INPUT !! - | eBay

I would love to be able to do it myself if possible.