all the win9x and win2k works fine with the io.
win2k pro is the fastest and of course would be more stable than win9x. someone at the post said it is so after experimenting with different os on the io.
the drivers would automatically install otherwise i would assume you can use the same drivers available for win9x for the win2k.
go with win2k if your harddrive have room for it.
i personally want to put in my win2k advance server, yup i own a copy of it. but my hd is just 540 meg large, so i can't go there.