iScroll2 is a modified trackpad driver that adds two-finger scrolling capabilities to supported pre-2005 PowerBooks and iBooks on OS X 10.3 and up.
Supported models include most aluminum PowerBooks introduced from 2003 to 2004 as well as most G4 iBooks.
Note: Models that have two-finger scrolling already built-in are not supported! These use a completely different, USB-based trackpad, the driver or which is not available as open source.
iScroll2 is based on Apple's AppleADBMouse-209.0.10 driver for the ADB-based trackpads found on older models, which is available as part of the publicly released Darwin source code (and covered by the APSL). The code added for supporting two-finger scrolling was written from scratch.
The installer will tell you whether your machine is supported or not. Alternatively, you can use this little script. Just unpack and double-click in Finder.
Note: Both the driver and this check may not work if you have another alternative trackpad driver (such as SideTrack or FingaMIDI) installed.
Models that are known not to be supported include all G3 and Titanium PowerBooks, the very first 12" PowerBook model, all G3 iBooks, and all newer machines that come with two-finger-scrolling built-in: The trackpads of the older machines simply lack two-finger detection capabilities completely, whereas the models that have scrolling built-in use a completely different, USB-based trackpad, the driver for which is not available as open source.
Note: As should be obvious from the version numbers, iScroll2 is still in its early stages of development, and thus likely contains bugs. If you encounter any issues, please don't hesitate to let me know. Please include a detailed description of the problem you're encountering, how to reproduce it, the relevant version numbers (iScroll2, OS X), the PowerBook or iBook model you're using and anything else that might be related to the issue you're reporting.
With that said, please get the current release from the download page.
The binary package includes a GUI installer. Just unzip the archive, double-click on the installer package and follow the on-screen instructions.
iScroll2 includes a preference pane that allows you to fine-tune the driver to your specific needs. Settings should be remembered across reboots and sleep, and on a per-user basis (i.e. each user on a machine can configure iScroll2 individually).
Unlike the "official" two-finger functionality available on later Apple laptops, all scrolling-related settings for iScroll2 can be found in the iScroll2 preference pane. iScroll2 will not enable the additional controls in the Keyboard & Mouse preference pane.
To scroll, just place two fingers on your trackpad instead of one. Both fingers need to be placed next to each other horizontally (not vertically, the trackpad cannot detect that). Some people get better results with their finger spaced a little bit apart, while others prefer having the fingers right next to each other.
iScroll2 provides two scrolling modes: Linear and circular scrolling.
For linear scrolling, move the two fingers up/down or left/right in a straight line, respectively, to scroll in that direction.
Circular scrolling works in a way similar to the iPod's scroll wheel: Move the two fingers in a circle to scroll up or down, depending on whether you move in a clockwise or counterclockwise direction.
In addition to scrolling, iScroll2 also supports mapping the trackpad button and the tap gesture to a specific mouse button. The trackpad button can also be remapped dynamically depending on whether two fingers are on the trackpad. This can be configured in the included preference pane.
To uninstall iScroll2, click the "uninstall" button in the preference pane, or download the underlying script here. Please follow the on-screen instructions to complete the deinstallation process.
For general discussion, please use the project's forums or mailing lists.