It's very easy to incorporate Windows XP Service Pack 1 into your Windows XP CD installation.
This way you don't have to install Windows XP, then patch it with SP1.
This guide makes it simple to 'slipstream' SP1 into your Windows XP and make it into a bootable CD.
This is perfectly legal for Windows XP owners and endorsed by Microsoft as a great way to keep your OS tip top.
The user guide is at:
SP1 Slipstream checked as working by Dirk Diggler 07/05/2003