Help! HP 530 notebook with XP PRO downgrade can't reinstall xp

OK, Check this out! I bought a hp-530 notebook from a retailer and had them install the xp pro downgrade, It did not come with os recovery disk so I ordered them from hp in case I ever needed them and now I find myself in need of reformatting c drive. When I do try to install os cd I get error message: D:\i386\WINNTUGP\NETUPGRD.DLL file is missing, I then close error message and the enter product key window pops up, I then enter my product key and it says my key in not valid, after this I manually extracted the D:\i386\WINNTUGP\NETUPGRD.DLL file from the cd and placed it in the hp program files folder, still can't install xp. The online chat rep summed it up to a corrupt os cd. Please Help!