If you are with NTL or Telewest or basically have a cable router, all you will need is a Wirless Router. This will then connect via a cable to your supplied modem and you're good to go.
If you have a connection through a BT line, then you will needan ADSL modem/router. You can box up your supplied modem and just use the modem/router.
Don't forget to read the manuals as you will have to configure the router and put protection on it. If you are struggling, we'll do our best to help.