When you install Windows XP SP1, you receive:

The Product Key used to install Windows is invalid. Please contact your system administrator or retailer immediately to obtain a valid Product Key. You may also contact Microsoft Corporation's Anti-Piracy Team by emailing piracy@microsoft.com if you think you have purchased pirated Microsoft software. Please be assured that any personal information you send to the Microsoft Anti-Piracy Team will be kept in strict confidence.

If the key that you used has been blocked by Microsoft, you will receive this error.

Microsoft recommends that you purchase a valid retail Windows XP product.