Tiger had two-finger scrolling.
It could be because your PowerBook still use the ADB (Apple Desktop Bus) trackpad (models in 2005 started using a USB trackpad, therefore having two-finger scrolling).
Check out this utility to add two-finger scrolling to your PB:
http://iscroll2.sourceforge.net/#checksupport, the installer will check if whether your machine is support or not so it's worth a shot.