Macs can read fat32 and NTFS partitions. The best thing to do would be copy the files to a new directory on your main HD. (if you have the room) Then you can reformat the external drive and do what you please with it. Make sure that when you use disk utility, you select partition, options and APM for Power PC mac or GUID for intel mac. If you select the wrong thing, the new external drive will NOT be bootable. Good Luck.