Dual booting Windows XP and MacOS X

(distilled from this helpful guide)...

As a precaution, disable all other disks in BIOS.

Install XP on NTFS
Shrink its partition to 40Gb (using gparted or PartitionMagic)
Add (FAT32) partition for future OSX

Boot OSX DVD
Disk Utility

• erase (Journaled) OSX partition
• verify it's mounted

Terminal

• diskutil list
• fdisk -e /dev/rdiskN (0 if other disks are disabled)

• print
  
• flag X (to make new OSX partition active (bootable))
• write
• exit
  

Install OSX
Reboot and remember F8!