Expanding information

I have a list of items and I'd like to have additional information about each appear when cursoring over it.  I've looked in the css manual about the visible/invisible properties, searched the Dreamweaver & php manuals, and just can't get it right.  If someone would help me get started I would be very grateful.  I create some text with a class with visibility hidden and one with visibility visible, but don't know how to get that attached to the item.  In fact I'm muddled about the whole process.  What I read seems to suggest I need to use absolute positioning, and the hidden text leaves a blank space on the page, which is not what I'd like. 

I know I've seen pages that have photos & when you mouse over a box appears to the side with information about the photo.  I'm not using a photo, just a list item.  I've done the hover to interchange 2 images the same size, but that's not what I'm trying to do here.

Maybe this is something that just isn't possible?