hi,
i have a first gen ngage and i don't have problems using isync on a dual g5 running 10.3.4
howver, prior to the 10.3.4 update it was buggy as all hell.
it would not sync my calender but would sync my contacts.
when you first pair the ngage and the icon pops up on the isync bar, click on the ngage icon and a drop down menu will appear, at the top of the drop down menu click on delete everything on the ngage and then sync opposed to merge data on ngage with .mac.
and if you are not running 10.3.4, my problems went away when i upgraded.
hope this helps.
chung