[Ti] Cross-platform a flash drive?

[FWPHOTO]

My son has an iBook but his school is all Win. Is there anyway he can work 
on his Mac in, say, Word, & save it to a USB flash drive so it can be opened 
& worked on with the Win machine at his school? I suppose he'd need to be 
able to save & open that file back up on his iBook when he got home too.

We have a desktop Win PC at home too that he uses now but it'd be a shame if 
he can't use his Mac to do his school work.

TIA,

Frank Wiewandt