Let me clarify. You CAN NOT run Windows XP SP 1 on BootCamp. Honestly, it says it all over the BootCamp site, in the ReadMe and right in the Assistant software. 😀😉
It might install, but the drivers won't. You will never have a fully functioning SP1 install on BootCamp. Buy Parallels if you want to run SP1.
The only thing you can do now is use the BootCamp utility to remove the partition you created, restart, create a new partition, and install an SP2 version. I tried the same thing for fun, and this is the only way that worked.