Technically it depends on whether or not your previous licenses were OEM-based or Full Package Product (FPP). If your licenses came with a PC you purchased previously, those are OEM-based and NOT transferable. If you paid for a full retail copy of Windows 98 or later, than the Windows XP Upgrade is transferable.
Here is a text snippet from one of many docs posted on MSFT's website:
9. Can I transfer my operating system license from an old PC to a new one?
ANSWER. Not unless it was purchased as a Full-Packaged Product from a retail store (i.e., Windows in a box). Current OEM licenses for all Microsoft operating system products are not transferable from one machine to another. The End User License Agreement (EULA) governs the terms for transfer of licenses. Some EULAs for copies of certain older OEM operating system products (i.e., MS-DOS®, Windows® 3.1, and Windows for Workgroups 3.1) distributed in 1995 or earlier may permit transfer of the OEM operating system software license under limited circumstances. (See Software Product Transfer section of your End User License Agreement.)