The only way to properly lock down Win98 is to cut the network cable going into the box.
At least with WinXP one has true user accounts such that kids in one's family can be given their own user accounts that have been neutered to the point where the kids can not install crap. Win98's user account scheme is for looks only. Also Win98 can not upgrade IE6 to IE7, and IE7 is much more secure than IE6.
it's OT but .. we have two boxes each in my family ..actually my son has two and I have 4 :)
XP pro exists on 2 of the boxes that are not allowed to connect to the outside world ..
IE anything is never allowed to connect to the internet ..only used for checking pages will display in it ( versions 6 and 7 are as standalones on the XP boxes )..Loathe XP ..like driving with the hood welded shut ..
but each to their own ..like you said too much money invested in software that is doze only to give it up entirely ..98II is safe but you do have to be the only one allowed on the box ..:)