yep its a talk talk one - its has got lights and things on it - both phone and xbox cable go into it and I cant go on line myself if my sons on his xbox and it has got LAN USB ACT LINK and a power light - I think I must be thick lol
By the sound of it and follow some more looking into it by myself and CheekyChick it looks like you talk talk modem is in fact a one port router... Which is a really really daft concept!!
my advice would be to invest about 40quid in getting yourself a proper broadband router and replacing your current modem with that. Then you would also be able to use your computer on the net at the same time as your son wants to play on Xbox live.