win98
dont be too concerned . there is nothing wrong with win 98 se or win me for that matter . you dont need much of a machine by todays standards for them and most soft/hardware is compatible and is easy to find . they might crash every now and then but when they do will almost certainly reboot without any damage and any problems that arise can usually be fixed.
nt4 on the other hand is:-
very picky about which hardware it likes,
only suitable for business environments,
and prone to suddenly giving you the "blue screen of death" . for which 9/10 times you have to reinstall the whole operating system