TrackPad Shaolin Buddah Finger
With the release of the newer Powerbooks, Apple has included an updated USB TrackPad (replacing the ADB TrackPad) and some pseudo-proprietary two-finger scrolling features. I say pseudo because it turns out that some of the older Powerbooks and iBook support the enhanced scrolling.
A few Mac hack sites have posted these app/hack links to get the enhanced scrolling features to work on pre-2005 Powerbook models, like mine (I have the first generation Aluminum 15"). iScroll2 based on the Apple ADB Mouse Driver and modified by Daniel Becker and SideTrack a replacement TrackPad driver from Raging Menace.
Download: iScroll2 Two-Finger-Scrolling
Download: SideTrack Multi-Button Scrolling Mouse