Here's what I'm trying to achieve (picture)

[mPeror]

When a link is clicked, a box will pop-up and load some information from a database. Each link will load different data from the database.

Is there any library/tutorial that can help me accomplish this?

[DreyerMedia]

http://home.4th-age.com/demos/tips.html

Here is a example that gives a tooltip when the mouse is over. Maybe you can edit it?

[Buddy Bradley]

There's this:

http://www.codylindley.com/blogstuff/js/jtip/

It uses jQuery but is easy enough to translate into regular JS.