You will need to purchase a mini DVI to HDMI cable, or a mini DVI to standard DVI then connect another cable DVI to HDMI so it connects to the TV.
If you want the sound to come through the TV make sure your TV has a dedicated sound input associated with one of the HDMI inputs, as the DVI cable does not carry the audio through it (HDMI to HDMI does).
Alternatly, you could take the digital sound from the Macbook using the dedicated port and connect it into a 5.1 surround system. Though you would only recieve true 5.1 if the content you where watching was encoded with surround.
http://store.apple.com/uk/browse/home/shopmac/macaccessories/cables?mco=MjQzMTY
You could also connect the Macbook to the TV using a mini DVI to VGA if your TV has that connection on it. Be careful to look at the supported resolutions on the TV when using VGA as you might not be able to fill the whole TV screen with your Macbooks output (1:1 pixel mapping)
I hope this points you in the right direction.
Rob.