thunderthor:
Win 98 and XP format differently (something about a bit that one has, and the other doesn't).
clorbach:
I've found that once you get a "unformatted" error, the next disk probably will also until you exit Windows Explorer and go back in.
If you are desperate for a floppy, take a large magnet (preferably in a different room) and rub it all over the disk. Then it will definitly need formatting. Sort of an instant "media restore"!