Which Dell? model and service tag?
The xp install disk often works for several models of Dell. I might have one or be able to find one online. The original Dell Dimension oem xp disk checks the bios and does not ask you to enter a cd-key on an actual dell of similar date of origin. By buying the Dell you have a license for the OS originally shipped with the pc.
If it is new enough to be under warranty, Dell will sell you one cheap. Out of warranty gets difficult.
Many Dells have a recovery partition available as a choice with the f-12 boot menu at the splash screen but if you repartitioned and wiped out the Dell recovery partition with the new install, you may have nuked it.
OEM cd-keys on the sticker usually don't work with standard retail install cd's. There are exceptions though.
Edited by Ken-in-West-Seattle, 03 December 2009 - 09:08 AM.