I/O Magic GigaBank external hard drive compatability

I recently purchased an 80GB I/O Magic Portable USB external drive. I would like to use it to transfer files between the MAC and a Windows based machine. I am able to copy files from each machine to the disk, but the each machine will not recognize files copied from the other (they will not appear in Explorer on the Windows machine or in Finder in the MAC). I/O does not presently offer software support for the MAC but indicated that they have heard that some MAC users were able make the drive work successfully on both platforms.

This drive is very elegant, you'd almost think it was designed by Apple. I got it at Office Depot for $129.00 after rebates. It's slightly larger than a PDA and is powered by the USB port.

Any suggestions on how to resolve this compatibility issue would be greatly appreciated.