External Drive Partition Scheme: OSX Bootable and windows read/write

I want to be able to boot (10.5.1) to a partition on my external drive as well as have a separate partition for backing up a windows XP machine. Is this possible?

I have a 500 GB external drive (usb and firewire400) and two laptops, Powerbook G4 with 10.5.1 and winXP.

The mac is low on disk space, so I'd like to run leopard off of a partition on the external drive but still be able to use the external drive to back up the windows machine. I've seen plenty of forums on how to boot to leopard on an external drive and have the Leopard DVD on a small partition. I also know how to set it up to have one partition readable by a mac (HFS+) and another partition readable by a pc (MS-DOS FAT-32). But to do this the partition scheme needs to be Master Boot Record (MBR). However for the external drive to be bootable it needs the APM scheme. This info is plainly stated in disk util when you go through this process.

Is there another way to do this?