hi, this is trent from dell, inc.... yup, we send out dell winxp OEM versions... it has a program that runs during reinstall that checks the bios for the service tag of your dell system. if you're going to use the same cd on a non-dell system, reinstall will ask you to enter the product key (which is written on the COA label found on the computer chassis). newly shipped systems have their winxp pre-activated, no need to activate nor re-activate them unless you reinstalled the whole winxp...
Vipre, I'm guessing that you have a Dell OEM XP Pro (or Home) SP2 CD, and re-installed onto a Dell computer. In this situation, your CD would have checked the BIOS during installation, found that you were installing onto a Dell computer and activated itself automatically without ever contacting Micro$oft.
There is nothing more to do. If this isn't what happened, your Windows Installation will certainly tell you about it soon enough and give you a phone # to bang your head against as you try to convince someone for whom Inglish isn't his first language that your copy of their software is paid for and legal...