mac <-> pc problems

I have a zip disk with data on it that was saved by a Macintosh computer. However, I am forced to try and retrieve this information by a zip drive installed on a PC. When I try to access the disk I recieve the message: "Disk in drive F: is not formatted." I assume this is because the data is in Macintosh format. Obviously, I am trying to retrieve the data without re-formatting the disk, as this would delete it. Does anyone know of a mehtod to do this, or of a freeware program that can translatate the disk for me, because as it stands, I can't even access the disk.