i was gonna say you cant do it on the old powerbooks if they're running stock, but you found that out anyway. i think you can do it on the G4 desktops if you upgrade the GPU to support dual-monitors, but other than that i think the hack is the only way to do it.
Tiger isnt the best OS for this kinda stuff.
i use a 14" apple monitor. like this one
and when i tried to use a VGA monitor in cooperation with it, i got what you just described lol.