You can transfer your addresses from the Address Book application to the new Palm Desktop. Open Palm Desktop. Then open the address list (Under View, or Shft-Apple-A). Next open the Address Book application. Drag your address entries from Address Book into the address list in Palm Desktop!
There does not, however, seem to be a way to transfer them back to Address Book.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011227233519701