TCP/IP settings are adapter specific, you'll find them under hkey_local_machine\system\currentcontrolset\services\%adaptername%\parameters\tcp/ip. Yes, when I say %adaptername% that is a variable for whatever Network Card is installed, meaning its likely a different name for each machine you have (unless you are lucky enough to have all computers using the same nic card). I think there is even an enabledhcp value you can create if you wanted to, and set it to 1, but again, its going to be in a different spot on each PC.
You really are better off walking to each machine and setting them to use DHCP manually. Realize that DHCP on 98 was far from perfect, and you will likely increase boot times on your desktops.
Matt J.
Please always take the time to backup any and all data before performing any actions suggested for ANY problem, regardless of how minor a change it might seem. Also test the backup to make sure it is intact.