Expanding/Collapsing Sections

You see this effect on lots of different sites. An excellent example of this effect can be found on http://fanball.com/ if you scroll down a little and look at their "Newsbreakers" section. But I'll explain this with an example most of you are more familiar with - Gmail. When you're viewing a message thread in Gmail, all messages other than the latest start off collapsed, and by simply clicking on the subject header the message expands to show the message body without having to reload the whole page.

That's the general effect I'm talking about but just in case it matters, my project doesn't involve email - just simple text and graphics. I want to have sort of a user profile of the month and as each month passes, have previously highlighted profiles listed below in collaped, compacted form. A clickable "region" like Gmail uses would be fine but I'm also fine with a simple text link that says "expand" or "more".

So how is this expand/collapse effect accomplished? Does anybody have any links to tutorials-for-idiots on this effect?

Thanks in advance

P.S. If anybody wants a Gmail account just send me a PM.