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Increasingly modems, both cable and ADSL, will not offer USB as a means of connection. As broadband speeds increase, the dedicated network card will always have the advantage over USB in reducing bottlenecks.
Assuming your computers have ethernet connection it's really rather simple.
First establish your connection direct between the modem and ethernet to the master PC. Remember to power down the modem and PC before plugging it all in. Follow the Virgin Media supplied set up of your account (you shouldn't need the CD).
This article may help.
Once you know you have internet working on your master PC then you can setup the rest of your network using your switch. Simply put run the windows internet connection sharing wizards. You do however require a second ethernet port on your master PC (the one that has the ethernet connection to the modem).
The alternative to the switch is to use a router in place of the master PC.