you did ARM the track?!?! thats the first thing I can think of.
the thing is also , I use a decent enough sound card (that supports asio) and well it's a different thing to using the in built soundcard which would have far higher latency normally.
Jed, I'm not clued up on macboook (well not these days :) ) , but I'm assuming your using it via XP emulation ? it should be a case of it's using it's generic driver.. the easiest way to test that is via audacity or sound recorder even.