"Formatted for the Mac" and FAT are contradictory.
HFS is the default format for the Mac; FAT32 is a Windows format.
If the disk is unpartitioned and all formatted FAT32, then both a Windows and a Mac should be able to read and write to it.
If the disk is actually formatted HFS+ (aka Mac OS X Extended), then you will need to either reformat the disk or install a utility like
MacDrive on your PC to allow it to read the Mac formatting.
If you're certain the disk is formatted FAT32 and your PC isn't reading it, you will need to copy all the data on it onto another drive or computer and reformat the drive for FAT32, then restore the data.