Problem is that 98 / ME don't have security features / access rights the way 2000 / XP do, so no you can't.
Since you can't afford to upgrade Windows(?) you might have to get by with creating a Ghost / Drive Image backup of a clean install, then restore that as needed. Of course to do this legally you'll need to buy either 1 copy of Ghost / DI per machine, or an Enterprise version that allows multiple machine use.