Internet Sharing using USRobtics Wireless Router & Dail UP

Am using a USRobotics USR 5461 wireless router. I have two desktops hard wired into the router and a wireless using wireless access. The desktop that is connected by dailup is running Windows XP. The other desktop is Windows 98, the laptop is running XP. How can I go about sharing my Internet connection. I know I need to change the router’s IP address and lock the IP address of the one desktop so that it doesn’t change, but I haven’t been able to get it to work with any reliability.

Thanks
Bill