This is the kit you need. You can call Crutchfield and see, but I already checked, it does say Pontiac. Just look at the pic and see if it looks like it'd fit. If nottt......... then............. go here and do all this.
http://www.crutchfield.com/S-jv5XGHSAFMo/cgi-bin/autoinfo/autoinfo.asp?lp=%2Fapp%2FCar%2FMyCar.aspx&sl=
Once you fill it out, it says "Free installation gear. Worth up to 99.92"
Then click "View all installation gear" and it will show you this
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
http://www.crutchfield.com/p_142GM1587B/Pontiac-In-dash-Receiver-Kit.html
EDIT: 24 MINUTES LATER.. (SHIT)
actually you'll also need this expensive adapter kit.
http://www.crutchfield.com/p_120993303/Chevy-Pontiac-Adapter-Package.html
Notice!! it cost 179$, but ifyou buy from that website, you get it for FREE.