Yes you can share that USB modem internet connection on one PC with other PCs over an ad-hoc wireless network, even without a switch or wireless router. This is made possible with Internet Connection Sharing (ICS), a network service/feature of all windows-based systems. The sharing can also be done just between two PCs connected using an Ethernet cross-over cable.
How Do I Share My USB Modem Internet Connection With Other PCs Without A Switch/Router, Over My Ad-hoc WLAN?
Steps:
1. Connect the USB modem (e.g. MTN 3G USB modem) to the host computer.
2. Enable ICS on the USB modem connection properties and select the network type through which you desire to share (e.g. Wireless Local Area Network connection)
3. Select the services you would want to run by clicking Settings. The basic services you need in order to access the internet are DHCP, DNS, HTTP, HTTPS.
4. Once this is done, your wireless card is assigned a static IP address. So before commencing the ICS setup, ensure the card is on DHCP so as to obtain the static IP address to be assigned. The static IP could be something like 192.168.137.1
5. Now its time to hook up other PCs to experience the sharing work! Note that ICS has to be enabled also on all PCs intending to access the internet via the host PC. Since we're using WLAN in this case, enable ICS on the WLAN card properties and select relevant services as done earlier on the host PC (DHCP, DNS, HTTP, HTTPS)
6. At this point, you are good to go! To test, first check the IP details on the host and network PCs using the "IPCONFIG /ALL" command on windows command prompt. Example is shown below of one of the network PCs. It can access the internet since a website (e.g. http://www.google.com.ng ) can be reached and responds when the PING command is used!
Go ahead and try it out, it works...!
Source: ezinearticles.com