I doubt XP protects itself against repartitioning. I've never used Partition magic but I believe that repartitioning NTFS is possible. See thread below for more info:
http://www.linuxquestions.org/questi...81#post1807181
Also do a "ntfs resize" in
www.google.com/linux. That will give you a place to start.
If you have the Rescue/Recovery CD/DVD available, and you have not customized your Windows too much, I would repartition the disk using some Linux live-CD (such as knoppix), leaving first partition (/dev/hda1) for windows. Fdisk, cfdisk or qtparted should be able to do the job. Then I'd reinstall WIndows with the Recovery CD and install Linux on the remaining partition(s).
It is _possible_ that the Recovery CD/DVD will complain about the new disk layout, but I doubt they are that smart
.