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?

OP here. Thanks for the replies.

Would there be any problem with partioning the drive with, say, 199gb of EXT3 and 1gb of FAT32, so I could install the fs-driver on a new computer or quickly install some spyware fix or something? Would all of the major OSes notice this and act as if it's two drives?

Also, is EXT3 reliable? I seem to remembe FAT32 sucking back in the Win98 days, and NTFS now seeming much more stable - is EXT3 nice and trustworthy?