provided the activation centre doesn't detect that the software has been installed on a new computer.
When you instal WinXP it creates a unique 'hash' containing information about the hardware configuration of your machine. If you alter the configuration substantially - say by installing a new motherboard - the automatic activator may stop the activation and ask you to phone a Microsoft activation operator so you can explain the situation.
In practice it all works well, and you'll have no problems. Enjoy WindowsXP.