Boot from the installer disc, after the first screen to select the language, go the Menu bar at the top of the screen, under one of the drop downs is Disk Utilities. Can't remember if back in 10.3 you had to go a screen or so past the language select.

You might want to go to the Partition option in Disk Utility instead of Erase, choose 1 Partition, Mac OSX journaled. I don't know if XPF modifies the boot blocks or not, so to be safe use Partition.