Internet sharing

My office LAN connection is based on TCP/IP.
Using CLient/server connection (NT/Win98) and manually configure IP Address.
The problem is I would like to share my internet connection from client-1 to other clients.
Pls let me know what to do, if possible I don’t want any ‘not-free’ software, just any software from Windows or any-third party software that is free…

Thank you