the prep packages seems to be slightly different from year ranges.. most important to check before you start is to make sure the wiring is hanging for the compressor, pressure switch, etc. if you have those, check the firewall to see if the evaporator and expansion valve are already installed. if you have that check if the condenser is there (i dont think it is on your model).
I have all three a/c lines and pressure switch if you decide to embark on this endeavor. I'll sell them to you.
Before I start down this path I'd really like to know if someone else has done it. I'm handy with the wrench, but I am definitely a novice. I've seen many posts for people doing this on newer cars with the prep package and it doesn't sound terribly difficult. Not having the prep package concerns me.
there are a few threads on it. your 04 will really not be any different. Sergey (i know i mispelled it but hes not on as much for me to remember) did it with the lesser prep package. he had to install more parts than most of us. I have all the pieces sitting here, but just haven't bought the belt to exchange it out.. so i have not installed it yet.
you cant tell/say if you have the prep package or not? look at the firewall on the passenger side, it there a box with a plastic cover held on the looks like it sealing two hose holes? and then reach in front of the block need the idler pulley (where the ac would go) and see if there is a wire tied up.. and also right near the intake there should be another loose plug.. if you have those three things i think you can install it easily enough.