Well you could either look at SSI (server side includes) to include your menu on every page and then you only need one copy.

As for the content appearing in the centre then you are limited to a)Frames (very bad) , b iframes (better), or c) just a normal page.

If its only a small bit of content you could hide and show elements etc but that soon gets messy.

Either way its not really a css question that I can help more with