Nothing you can do without a good key.
You can try Magic Jellybean Keyfinder
to see if it can get the key for you. You would have to slave your drive to another computer, either in a external caddy or use a universal USB drive adapter.
From their FAQ:
Q: Can I retrieve the product key from a non-booting Windows installation?
As long as both Windows versions are 2000, XP, 2003, or Vista, you can use the Load Hive function. You will have to slave the drive and point the Keyfinder to the non-booting Windows directory.
Q: Why did the hive load fail?
1) Are both versions of Windows 2000, XP, 2003, or Vista?
2) Are you pointing it to the dead Windows directory? It will fail if you try to run it on your currently running Windows directory.
3) Are you running the Keyfinder with Administrator rights? Right click on the Keyfinder and click "Run As" and put in the administrator information.