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.