I have partitioned my ipod mini 4GB and it is now 2gb on mac and 2gb on windows.
I formatted the ipod on the mac and formatted it on a windows machine and they work on both fine!
my ipod is windows formatted, and the only thing i can't do on my mac is rename it. other wise it acts just like a mac formatted ipod, only now i can use it to transfer large files back and forth between my to computers.