Still don't really understand what you want to do 100%
Are you saying your 'mainframe' is running Windows 98?
Sounds like maybe you want to allow others to connect to this machine over the internet?
If I am close, you are looking for a VPN (virtual private network). Creates a tunnel through the internet for secure use of the resources on the server. Versions of windows based on NT (2000, XP, NT) have a built in VPN server -- not sure about 98, but I think it does. If that is what you want to do, search the net for win98 VPN or post back.