Firstly, if you have one "host" PC connected via a modem to the internet and are using "Internet Connection Sharing" to provide internet access to a "client" PC, in order to add an additional "client" PC wirelessly, you need to be running Windows XP in the "host" PC and you need to "bridge" the two network adapters - the Local Area Connection and the Wireless Network Connection.
1) In the Network Connections folder, right click the actual internet connection (modem connection), select Properties and then the Advanced tab. Untick the box "Allow other network users... etc" and click OK.
2) Highlight the Local Area Connection and the Wireless Network Connection, right click and select "Bridge Connections".
3) Reverse step (1). Right click the actual internet connection (modem connection), select Properties and then the Advanced tab. Tick the box "Allow other network users... etc" and click OK.
The Network Bridge will now have the IP address 192.168.0.1 subnet mask 255.255.255.0 and the individual adapters no longer have an individual IP address. Both "client" PCs should get their IP addresses automatically from the "host" PC via the bridged network adapters.
<<< however while the laptop is showing the network as available the pc does not show any wireless network >>>
Is the PC's Wireless Network Adapter definitely configured to work in "Ad Hoc" mode (which some manufacturers call peer-to-peer mode)? If so, try disabling and re-enabling the adapter to see if it finds the Ad Hoc network. It can be very fiddly to get an adapter to find an Ad Hoc network initially, a reboot might also help to find it.