I was tearing my hair out at this one.
If you use an answer file to install Windows XP, you might find your install completely fails. This is mainly because Apple does some funky stuff to the partition map, and doesn't format the partition properly. As a result, you may get errors about a corrupt hal.dll if you repartition to NTFS, or a disk error if you use the default FAT32 partition that Apple creates.
The solution? Rip out the answer file and do a reformat of the Boot Camp partition before you install.
[robg adds: I had no idea what an answer file is, so I included the link to Wikipedia's entry on the subject. An answer file seemingly automates the Windows XP installation process.]

