like this, and notice how cheap! Every girl should have one.
Solder. (This is the "glue" for your "glue gun")
18 Guage Speaker Wire, this project required just over 100 feet of it, but you may not need this much. Still - it's pretty cheap. I found this at my local Lowe's in the section with the telephone and other cable.
tutorial on how to use a soldering gun, but it works just like a glue gun. Instead of the glue being pushed through the hot nozzle, however, you have to hold the solder against the tip to melt it. CAREFUL HERE: don't get any solder between the positive and negative circles, they have to be kept separate.
NOTE: transformers can go bad, so make sure you've got access if you need to replace it. I'm going to have to cut an access panel in the top of the bookcase, and cover it with a thin piece of wood. I'm going to be building the top of these bookcases up with crown molding, so I need to be able to access the transformer another way.
I should have just plugged this into the outlet down at the bottom of the wall, but at the beginning of this project I thought that I was going to install bookcase "lamps" at the top of each one... this design change made a little more work for me but it's ok. :) Here is the post where I showed the wiring for the new switch and outlet (these LED lights are controlled by a switch I installed in the wall first.)