Hi, firstly, Welcome to the forums
It is not a network hub you need to share internet accross on your computers, but a cable Internet router instead.
Your modem plugs into this and you then connect each computer to the router.
The only way you could use the two modems is if you had registered each modem and pay for them both each month.
Modems need to be authenticated and registered to you from NTL so swapping cable modems to another one will probably not work.
If you didnt want to get a router to share the connection, you dont need to have two modems. You could pay for a second IP and use the one modem to control two connections. This will cost you more each month and you would be better getting a router to share your current 2mb connection to each computer.
Im sure there will be more people to help you out shortly, but thats my quick take on things.
Good luck. I hope you like it here and decide to stick around.