Partitioning a bootable Flash drive

Solution 1:

Unfortunately, the windows accessable partition must be the first partition on a thumb drive or windows will not mount it. Linux installs can get around this limitation by putting the bootloader configuration files on the windows partition and everything else on the second partition. I'm not sure if you can do this with Mac though. My Mac is to old to try (as it is PPC based.)

Solution 2:

The Geniuses at the Apple stores use external USB drives that boot to Mac OS X. So it's possible.

iHackintosh shows you how. rEFIt helps to make drives bootable for Mac and Windows. You'll need something like it in order to keep the two partition managers (Mac and Windows/Linux) in sync.