Partition Magic is Windows only, once installed it creates floppy disks versions also. If you had owned it prior, you could have booted the system with the floppy version.
Can you mount the Windows partition under FreeBSD, and see if that mentioned file is missing, if so, then replace it if able to, which might require some prgoram to write to NTFS, unless you using FAT on the XP filesystem. Then see if the system boots afterwards.
You can partition the system with qtparted - which looks very similar to Partition Magic, plus its free and available on a bootable CD. You can download it from
http://www.sysresccd.org/