someone has to do it straight....
if he's only got a week, you can spend that all in instabul and the locel area. the main things are the topkapi palace and the blue mosque, etc. lots of cool things.
the food absoultely rocks and if you head down the coast the best greek and roman cities are there.
also, check out the bazars, they are pretty cool. not a lot of bars and stuff (muslim country) but there's some cool stuff over by the university.
i'd reccomend checking out cappadocia if you have more time but you cant really go wrong throughout most of turkey.
i spent a month there travelling with an ex-girlfriend and it was one of the coolest places i've ever been.
also, my spelling sucks