Apple has released Magic Trackpad and Multi-Touch Trackpad Update 1.0. Release notes state that the update:
“includes the required software to use Magic Trackpad. The update also installs the three-finger drag gesture and inertial scrolling for Mac portable computers, as listed below. This update also installs a Trackpad System Preferences pane for configuring Magic Trackpad on Intel-based Mac desktop computers that support Mac OS X v10.6.4 and above.”
This knowledge base article lists Macs that support inertial scrolling and three-finger drag gestures.
The new release is available through Software Update or via this download page.
This update requires Mac OS X 10.6.4.