Of course it won't work anymore. Every XP cd has its own Cd-key, otherwise how could Microsoft make money?

Your could go buy another XP cd by paying a high amount, or, maybe, Would Dell has the reservation of your OEM XP cd 's cd-key? You had better turn to Dell for help.

 What't more, are you individual users? If so, I suggest you should buy another XP pro ,because the XP cd provided by Dell for individual users most are HOME EDITION, which is less safer and available than pro.

Isoku,

Your Windows XP Product key is on a sticker on your computer (on the side of desktop systems, on the bottom of laptops) if Windows XP was installed on the computer when you bought it. If you buy another copy of XP it will have its own product key and a retail version of XP will install on a Dell system without a problem. A Windows XP product key is associated with a specific CD, whether that CD is a retail full XP or upgrade XP or a Dell OEM XP.

If Windows XP was not installed on the system when you purchased it but is still installed on the machine you can extract the product key of the installed copy by downloading Belarc Advisor from here and running it. It will also give you the product keys of any software that is installed.

No - The Dell CDs are whatever you ordered.  If you orfer XP Pro, you get XP Pro.  If you order XP Home, you get XP Home.  There is no known safety issues between XP Pro and XP Home.