FWIW, iScroll2 only works on recent Powerbook and iBook models that have the same trackpad used in the new Powerbooks. (Which is nearly anything 2003+) The iScroll2 installer will check for you.
That said, Sidetrack has more features but costs money. Personally I use iScroll2 because it works with my Powerbook, and that I never enjoyed having a scroll wheel at the side of the trackpad.
I still remember Macnutt.