Get yourself a nice big external firewire hard drive. You're going to want one to use with Leopard anyway, so you can use Time Machine. (Time Machine will probably not back up to a partition on an internal drive; it's looking for an external drive.)
Use Disk Utility (you can do this with Tiger) to repartition the drive. As you do the repartitioning, take great care to specify the correct partition scheme! If you're using a PPC machine, you want the Apple Partition Map (the default). If you're using an Intel machine (because you have no PPC machines), you want the GUID partition scheme; it is easy to neglect this step, and if you do, and you accidentally use APM, you won't be able to make a Leopard bootable disk. We suggest three partitions:
- A 10 GB partition to hold the clone of the Leopard DVD.
- A 30 GB partition to hold the Leopard system.
- All the rest to hold Time Machine backups.
- As described in the earlier tutorial, insert your Leopard installer DVD into the computer and make an image file from it. Now "restore" (clone) the image file to the first partition on the external firewire drive.
The first partition on the external firewire drive is now bootable: it is a clone of the installer DVD. So boot from it! The effect is just as if you had booted from the installer DVD: the installer will offer to install Leopard. Do an erase-and-install onto the second partition of the external firewire drive.
At the end of the installation process, the installer will automatically reboot the computer from the Leopard system it just installed on the second partition of the external drive. You will have to go through the usual kerfuffle about creating an initial admin user, declining the opportunity to subscribe to .Mac, etc. When you're all done, you'll be running Leopard from an external drive.
You should probably immediately use the Spotlight and Time Machine system preferences to set things up correctly. Your goal here is to prevent the computer from bogging down (and the fans from spinning up) by immediately indexing and backing up a bunch of unnecessary stuff.
You now have an external firewire drive that can boot your computer into Leopard. Remember to "put away" this drive properly before turning it off or unhooking it from the computer!