Whats a good resource for DHTML tutorials and lookups.

I'm making a script that will show a <div> with information by modifying its visibility on mouseover/mouseout.

But something tells me I should not be making one Div for each block of information I want to show... When I do this they take up the same amount of space as if they were all visible at once.

If you want to take a look my project is here:
http://www.xio.no/kunder/flybussen/portal/v7.php

At the moment it looks a mess, so any help would be appreciated!