Can I run 2 OS on 1 HD? OSX10.4 & OSX10.5

Odd situation but can I have OS 10.4.9 and OS 10.5 both on the same Mac with the option of which to run in, selecting it though System Prefs and Startup Disk mode?
I had a Powerbook G4 that ran the 10.4 and the cat knocked it to the floor. I can still access the hard drive but other issues need repair. Rather than do so I replaced it with a matching used PB G4 that has a clean install of 10.5 on it. I have applications on the 10.4 system that will not run on 10.5. For $$$ reasons I do not want to update the expensive programs, nor do I want to completely remove 10.5 on the newer machine. I have full backups on both. I would like it to work like the old OS9 and OS10 machines, that you could select through Startup Disk mode. Possible?

You can indeed have two operating systems on the same hard drive as long as the computer meets the minimum specs for the operating systems. I had something like that set up when I first started writing for ATPM. It's a decent idea especially when a new OS is released and you want to upgrade but have software that hasn't been updated yet.

Each version of the system software needs to be on its own partition. Also when you are deciding on the size of the partitions make sure to leave enough blank space on each partition for the virtual memory swap files.