there is a simultaneous thread regarding this topic..
http://taperssection.com/index.php?topic=40962.0but i would just load your software, (get your jb3) connect the jb3 to the mac usb port, hope the jb3 turns on (is found by the mac) then if it doenst automatically connect and show you the harddrive in the XNJB window, go to the Jukebox menu and click Connect. you should then see it in the XNJB window and be on your way. make sure to disconnect from the same drop down menu after transferring the files, and dont let the jb3 turn off after the file transfer is done, cause both will probably erase your files from the mac. (not the jb3, usually)
also, sometimes my desktop has a problem keeping the files once they are transferred, but my laptop works flawlessy although somewhat laboriously. strangely, both OS's are 10.3.9, so who knows whats up there.
you may also want to join the yahoo group jb3 and find some threads there that might help.
good luck, and dont get frustrated the first run.