If you have a Dell PC that was sold with a Dell OEM license for XP, and it's failing the Windows Genuine Advantage, you should contact Dell. They are responsible for the version of XP that they sold you, and I'm sure they'll fix the problem.
Similarly, if you have any other PCs with OEM software, I'm sure the system builder would anxious to help you resolve this issue.
If any of the PCs have boxed retail-package XP, then Microsoft would be directly responsible and, again, I'm sure would like to hear about the problem. Microsoft is gradually phasing in their new "Genuine Windows Advantage Notification" program, after testing it in some European countries, and it there are issues, I'd bet they'd want to get them fixed ASAP before continuing with more deployments.