This is not a legal issue, it's just a driver compatibility issue.
There are a couple of options for you.
1. Create a so-called "slipstreamed" installation CD of Windows XP that contains the SP2 and use this one instead of the original XP CD. This is entirely legal, by the way, and sanctioned by Microsoft.
Here is one of the guides that explain how to "slipstream" XP:
http://www.winsupersite.com/showcase/windowsxp_sp2_slipstream.asp2. You actually don't need BootCamp for anything. It's just a GUI that's supposed to make your life easier. The only problem is that you need a partition on your built-in hard disk with the right signature, so that the Mac's BIOS accepts it as bootable. On an Intel Mac, the correct type would be "GUID Partition". You can set this under "Options..." in Disk Utility when you have selected the disk (not one of its partitions) and then chose the "Partition" tab.
Vista and XP will see this GUID partition and will be able to install onto it. Just do not use Windows' own partition utility. Only format the drive. DO NOT PARTITION IT IN WINDOWS.
I have never tried to boot from an SP2-less XP disk on my Mac. There is a chance that for some reason it won't work. The safer bet is to create a slipstreamed CD and go from there - it saves you a lot of stress.
HTH,