Do you have to have the MS branded one?? If so there is another thread in this forum showing you how to get one from ebay. I think this a xbox to breakout box cable, so you still need a standard phono-phono component lead, + whatever audio lead you choose, to connect to your TV/Home Cinema system.
Otherwise I would recommend the equiv aftermarket component cable I got via e-bay from the states. Single cable - no breakout. With current exch rates cost £5.65 inc P&P and only took a few days to get to me. Reasonable build qual, Gold plated connectors - Works a dream in any hidef resolution. Can PM you the link if you want.