Sharing Internet Acsess

I have a PC with WinXp, having acsess to Internet through dial-up connection. Each computer in LAN has IP adress (from 192.168.1.1 (Above pc)-up to 255 with subnet mask 255.255.255.0).When I try to setup sharing Internet connectionon, pc with WinXp changes its IP adress to 192.168.0.1. Why it’s happen ?
Thanks…