Disk Utility appears to let you shrink the Mac OS partition. It is not obvious whether it expands the Windows partition. If it doesn't expand the Windows partition, then this does not solve your problem. 🙂 If it does expand the Windows partition, it may or may not delete Windows (I'm guessing not, but that is an uneducated
guess the consequences for which I refuse to be held responsible). Even if it does not delete Windows, it may render Windows unbootable. The issue with Windows--at least if you formatted the Windows partition NTFS--is that once you've installed Windows, the Windows partition contains a file C:boot.ini which, believe it or not, tells Windows where the Windows partition is. If you resize the Windows partition, then the data in boot.ini will surely be wrong, and so Windows will no longer boot, at least until you figure out how to fix boot.ini manually which may be as simple as running "repair" from the Windows installation CD.
The good news is that the place I learned this is
http://www.twocanoes.com/winclone/ which contains a free utility for backing up your Windows partition, resizing your Windows partition, and other Windows partition tasks. So if you don't trust Disk Utility to the task, and you do trust WinClone, then you can use the latter.
Whichever route you take, back up early and back up often! Both partitions!
