File system for external hard drive?

Potentially stupid question.

Buying a HD and external enclosure. I use Ubuntu/Win2k on one computer and WinXP on the other.

I should be formatting the HD as a FAT32 drive if I want it to work with everything, right?

>>8
you don't have do defragment a ext3 filesystem, because it doesn't get fragmented anyway unless its completely filled up. in that case defragmenting isn't possible anyway.