How to format a USB memory stick in FAT32 using a Master Boot Record (not GUID Partition Table)
From Tech-Wiki
Windows can not read a disk formatted using a GUID table.
Using ‘Disk Utility’ select the usb memory stick. Within the Partition tab select MS-DOS (FAT) as the format. Within the Options area, select Master Boot Record (as opposed to the default GUID Partition Table).
A better format that is truly cross-platform (mac, windows (xp needs a patch) and linux) is ExFAT – also supports very large file sizes.