To confirm the Windows Installation CD Product Key, you will not have anyhting available via Control Panel that can assist. You can get this information of you use Magical Jelly Bean Key finder
www.magicaljellybean.co
Call Compaq and advise them your Product Key and they may be adble to send you a Recovery CD set, Thgis amy cost a few dollars, but less than a full retail version of XP
If not, then check your version of XP: was it an early installation or one with SP1 included. Then ask a friend to borrow their installation CD and use your key
If you do this, then make sure that you also copy across to your Hard Drive the folder I386 after Windows is running. This contains all the installation information should you need to reinstall Windows again, then open that folder and if in Windows run WINNT32.EXE or if in DOS then run WINNT.EXE