I have updated the motion sensor software available from kernelthread.com (AMSTracker, AMSVisualizer, StableWindow, and AMS2HID) to work with updated versions of Apple's motion sensor driver. The software should now work with Mac OS X 10.4.3 -- both on PowerBooks and iBooks with motion sensors. I say "should work" because I have not tested the software myself -- I am currently traveling and have no access to a notebook with a motion sensor.
Link to Updated Apple Motion Sensor Software