FAT32's really your only option unless you buy MacDrive. You might be able to use a Linux/Unix format too, assuming that somebody's made a Windows driver (that might not be the right term) for it.
here said windows 98/me can format fat32 larger than 32GB.
http://www.abit-usa.com/faq/mb/2002031801.php
98/Me maybe, but this is for XP and Xp can not format a FAT32 drive larger tan 32GB
You could use EXT2 file system.
Not natively supported on Mac or Win, but drivers are available for both. EXT@ is used in Linux, so with the 2 drivers you would be able to use the drive on Window, OS X, and Linux.
No 4GB limit, etc...but a little extra hassle...
Mac Driver ---> http://sourceforge.net/projects/ext2fsx/
Win Driver ---> http://www.fs-driver.org/download.html
Just passing on an option...