[Halcyon]

Basically there is no need for you to pay an additional broadband connection. Save yourself the money and share the connection you have. This is what a lot of people do and is where the word "router" comes in as this lets you sperate your NTL connection.

Im guessing at the moment you have your NTL modem that either hooks up to your PC via a USB connection, or an ethernet cable into the back of your PC.

A router lets you share a connection and wireless ones lets you do this without having to run cables all over your house.

You dont need to have a wireless ethernet card in each PC as the one near the router could be linked via normal ethernet cable.
If you dont dont connect via ethernet, an ethernet card costs about £10 and fits into a spare PCI slot in your PC.

Just have a look behind your computer to see what sort of way you are connecting your PC to the NTL modem.

You would then simply need to put a wireless network card into your son's PC and these can either be put in to a PCI slot or be connected externally.
The wireless router would connect to your own PC via ethernet wire and then you hook up the NTL modem to the router.

It should cost you about £50 in all. And then you know that you are only paying one connection, and not 2, which saves you money, and you can use it to transfer files on your own network too.