Custom Category Pages

I’m trying to force wordpress to function as a CMS and I have determined that using categories would be best so that I could collect a bunch of posts on to one page and they could each have their individual comments and what not. What I want to do is have it so that when you click on the category link in the sidebar, it pulls up a page that lists all the posts in that category and has some content specific to that page above all of it. Like an explanation of what the category is about or something. Can this be done, and if so, how?