You can try to find somewhere to download the bootcamp beta for tiger, but if you can't then you can just install windows without using bootcamp, and find leopard bootcamp drivers.
You can install windows still if you partition your hard drive with disk utility. You would have to format the drive as FAT and then boot into a windows install disk and install windows on the empty partition. If the partition is bigger than 32GB then you are going to have to format it as NTFS during the XP install. After the windows install completes you would then have to hold the option key at startup to choose between the two.
You will still need the bootcamp drivers, but these can be the leopard drivers because windows doesn't know what other OS you have installed. You would have to find some way to download the bootcamp drivers, like I know torrents exist that contain these, you just have to search for them.
All bootcamp is is a GUI that allows you to partition your hard drive and provides the drivers to make the hardware work in windows. You don't need bootcamp to install windows so if you really want windows on your mac you will have to find some way to get the leopard bootcamp drivers and install them after you install windows.
Remember: You should
always back up your drive with something like
Carbon Copy Cloner before you do any disk maintenance. This is so you have a bootable copy of your OS X install so if something goes wrong with your internal HD, you can still boot from the external HD and have all the files intact. You can even do work on the internal HD from the external so you can fix the problem or reformat the internal drive. And then clone it back with CCC from the external.