Create different partitions on external drive (Score 2, Informative)

Create different partitions on external drive, one for example EXT3 and other FAT32. EXT3 would be large and FAT32 would be very small couple of megabytes. On smaller partition you would have EXT3 drivers for Windows machines. With this you would be able to access EXT3 from any machine. You could also try different file systems in same way.