Try Belarc Advisor.

The product ID shown for windows XP may differ from one on the sticker on the computer's case.This is because the ID shown by Belarc Advisor may be the volume licensing ID used by Dell to install Windows XP. The ID from the sticker should be uesed if a reinstallation of Windows prompt for it.

Speak to the Dell technitian and explain your situation.

 

If you have problems Activating your reinstallation of XP call this number (Microsoft) to get it done.

 

1-888-571-2048    Toll-Free USA

IF you are installing a Dell OEM Windows XP CD onto a Dell Branded PC you will not need a CD Key. They are all BIOS locked and Pre-Activated.

 

pcgeek11

Also, to add to PCGeek11's response, each install of Windows XP (the CD you were sent from Dell), can not be used on another machine, irregardless if the original machine was sent to a scrap yard (scavenged for the gold thread in the circuitry along with some non-biodegradable elements (mercury is at the top of the list)...then the hull of the computer run through a grinder and spit out in thousands of small pieces...that license is forever tied to the "Unique ID" embedded in the cpu chip. 

 

Microsoft went to great lengths to come up with this new "Genuine Advantage".  When you run Windows Update, you are prompted to download/use the Windows Installer, they call it Genuine Advantage to make sure the software is not pirated.  Dell along with other OEM manufacturers pre-registers a license for your machine, at the factory (they have a blanket policy/agreement with Microsoft to allow for this on a adhoc basis).  This way, you can't then take that "reinstall" CD and use it to upgrade your son's machine, or who/what ever machine you want to.

 

Hopefully the replacement Laptop you were granted, was by Dell and "pre-registered" the license for you...which would then allow you to reinstall from that CD.  As for calling Microsoft directly to acquire the proper CD key, they'll only tell you to call your OEM manufacturer...in this case, Dell...if I'm not mistaken. 

 

On a side note, if the laptop is from Dell and the CD is also from Dell (assuming the OS is the original that was installed previously), Dell usually puts the CD Key/License key on a sticker that has Microsoft seals and watermarks all over it, that is located on the side of a desktop model, or on the underside for laptops....give it a whirl.

 

I hope this helps.

Cheers!