Got my new K750i yesterday, and today I decided to figure out how to hack iSync 1.5 (10.3 Panther) to make the syncing work. I've published a working how-to and added a screendump as "proof." Many people seem to have questions around this, and I've only seen solutions for Tiger, so please enjoy!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050521191932641