I use a BT HomeHub 2.0, as it came with my broadband package. My whole house is wired with 100mbs LAN and my broadband speed is only about 12mbs so it is pretty sufficiant. The homehub uses a 15v transformer, which is connected straight into one of the supplys sockets. I extended the length of the cord to reach from the garage loft into the house using some old telephone cable. This is fine as it is a pretty low power device.
Thats about all there is to it, just make sure you didnt mix up the polarity of the connector by testing it with a multimeter, for the homehup the inside of the connector should be positive.