Darwin handles the bootloader for OSX its equal to NTOSKRNL for Windows.
To begin dual booting, install Windows XP on a fresh HDD formatted for NTFS.
Download and install Acronis Disk Director and make:
PRIMARY+ACTIVE partition for OSX86.
While still inside your Acronis Disk Director Boot CD, set partition type to:
SHAG OS (0xaf).
Reboot using your OSX86 DVD. Before installation, pick TOOLS-> DISK UTILITY.
Find your OSX86 PARTITION and ERASE. Pick HFS+ Journaled.
Pick your patches and reboot when finished. Then edit your boot plist.
You will need to add a TIMEOUT of 5-INFINITY. This will then show you XP+OSX.
There are a few minor steps I did not mention because this is NOT a guide.
There are many guides online that are more detailed.