Compact just means you will have a lower gear up front. Its a great compromise over a triple (better shifting, less weight, and the one that matters, people won't snicker at you). Your chain should be fine, it'll just need to be resized, and you MAY need new derailleurs if the ones you have can't handle the tooth difference (16t) of a compact. I personally have a compact on both of my bikes, along with a wide range cassette on the back. I don't care about bragging rights, I like being able to comfortably make it over hills!