Since Nytmare hasn't updated his VIN decoder in quite a while, and since it doesn't work with Firefox, I have taken the liberty of copying it, fixing it, and putting it on the GA Fiero Club website. You can access it
here.
I have begun to update the engine decoding (it only had the two Fiero engines and a few other 4-cylinder engines before, and just showed "?" for all others. I have added the 3.1 PR, the 3.4 PR, the 3.4 DOHC, and the 3800's from 1988 through Series II. So now, if you enter this VIN:
2G1WP14X4N9148130
it shows a 1992 Chevy Lumina Z34 with a 3.4 DOHC engine.
Also, I found another site for looking up RPO codes
here. There's a few omissions in it (CJB isn't there), and a few mistakes (LR8 (iron duke) is listed as 2.8 liters). But it's mostly ok.
Edit: Oh, yeah, the VIN decoder works on Firefox now.
[This message has been edited by TopNotch (edited 08-07-2009).]