Sorry Ty. As far as I know, Time Machine is exclusive to Leopard. There are a couple of hacks people have developed, but unless you're really comfortable with Command Line I wouldn't mess with them.
One option you could go with is to run a program like Super Duper or Carbon Copy Cloner to clone your hard drive to your external. Only problem with these are you have to run them in the foreground and not make changes to the system while their running (changes could lead to a corrupt backup). Best to run them at a time when the system isn't being used.
Zero One Media Center
Apple Certified Hardware Technician