One of the features offered by the new Powerbooks is a scrolling trackpad. However there has been some speculation about whether this was a hardware or a software upgrade. If the new functionality was only a software tweak, it would mean that those of us with older Powerbooks might stand a chance of acquiring scrolling trackpads of our very own.
Well it looks like it's mostly a software upgrade, and Daniel Becker has come up with a hack to activate two-finger scrolling on supported pre-2005 PowerBooks and iBooks, which are those with "W-Enhanced" trackpads. Don't know whether your trackpad is W-Enhanced? Don't worry, he's also provided a script to allow you to figure this out.
Update: I've now installed the driver and it works without a hitch, I especially like the fact that it can turn left clicks into right clicks whenever two fingers are on the trackpad.