Problem: Unable to activate Windows XP using the correct activation code.

I have a Dell desktop originally supplied with Windows XP Pro (2001, prior to SP-1 or SP-2). The original CDs are long gone. I have created an Unattended Install disk slipstreamed with SP-2 using the CD for another system and it installs XP Pro perfectly.

The old Dell has a sticker proving the Windows XP is legal and legitimate, but this activation code will not work with the slipstreamed disk.

I have phoned Microsoft attempting to activate using the legitimate activation code, but they refuse to activate using that code and tell me I have to call Dell. Of course when I call Dell, they tell me I have to call Microsoft.

I have legally-purchased licenses for my software and I would prefer to use the correct codes, but Microsoft seems dead-set on stopping me. Any advice?

You need the CDs that Dell provided you with in order to use that product key on the Dell sticker. It will not work with any other copy except with the one from Dell. However, I believe that Dell CDs use a generic product key that only install on Dell systems, so that key would be unecessary when installing using the Dell CD.