You need to enable "Internet Connection Sharing" on the actual internet connection (modem connection) in the "Host" PC. This will automatically configure the PC's network adapter (that connects to the "Client" PC) with the fixed IP address 192.168.0.1 and subnet mask 255.255.255.0
The "Client" PC's network adapter is set to get its IP address automatically, which it does from the "Host" PC. If you have been networking without Internet Connection Sharing, you may have allocated a fixed IP address to what is now the "Client" PC, so this setting should be changed.
Any firewall software needs to be configured to allow access to the networked computers by entering their IP addresses in its "trusted" area. Also, if you should be using Zone alarm in the "Host" PC, you need to reduce the Internet Zone Security level from High to Medium or I.C.S. traffic will be blocked.