First off, welcome to Linux, I hope you enjoy it.
Windows is really picky about how it needs to be started, I don't know about the macbook aspect, but this is what I had to do to get my desktop to boot windows.
(my entry in /boot/grub/menu.lst for windows)
Code:
title Microsoft Windows XP Professional
root (hd1,0)
savedefault
makeactive
map (hd0) (hd1)
map (hd1) (hd0)
chainloader +1
The "make active" "map"s and "chainloader" lines are all necessary, and the grub website can explain it much better than I can. You could probably copy the above, change the root (hd1,0) line to match your partition scheme and be ok.
As with everything, you can make things ALOT worse playing around with this, so read the documentation and be careful.
(and keeping a good live cd on hand can go a long way towards making it easy to get things back when you mess up)
Grub's documentation page on multi booting with windows
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