You're going to have to aquire some stereo removal tools... You can see the ones from crutchfield here:
http://www.crutchfield.com/S-9mnWOwFoxKY/cgi-bin/prodview.asp?I=120869001
Just be careful... I hate to admit it, but those things sent me to the hospital... they're made out of really cheap stamped steel, and the edges aren't deburred... I slipped while trying to remove my deck, and it gave me a really, really deep slice... My fiancee' made me go to the medic when I was getting dizzy from a lack of hydraulic pressure