That link leads to an awesome install for sure.
I didn't go that route though. I left my AM radio in tact and attached to the dash speaker so it still operates in it's original design (minus the AM powered rear speaker).
The real stereo is not a stereo at all. I have NO headunit installed and instead I use my Ipod or phone as the input source. This allows me to not only have access to modern music storage but also, navigation, hands free phone use, and what I really like to do on long trips is to listen to movies (Netflix) through the speakers as I drive which the passenger can view on the phone screen itself.
I bought a Pioneer 760watt 4 channel amp, 2 Kicker 6x9's, and 2 Kicker 5.25" speakers, amp install kit and an adapter that takes the signal from a headphone jack and turns it into an RCA level input for the amp. All in with speakers, amp, and all the appropriate install components, it ran me about $250. Most headunits alone cost that much.
I installed the amp upside down under the package tray area in the trunk which keeps it completely out of sight and allows it plenty of airspace to keep cool. Then by using 1" spacers made from the Kicker speaker grill covers for the 6x9"s, I mounted the 6x9"s in the stock rear locations mounted from the trunk side. Then I mounted the 5.25"s up front in some extra kick panel covers I had laying around.
Then I ran the wiring for the amp, the speakers, and for the IPod input. It was pretty easy, with a bit of planning, to keep the wiring separate and organized.
My Ipod connection comes out right beside the console on the driver's side. I actually keep it connected to the "female" seat belt connection which allows me to easily access it. Volume is controlled by the Ipod or phone which, when connected, stays put right on the console.
I will post a pic to show you what it all looks like in but basically there is nothing to see. The whole set-up is hidden other than the 5.25"s mounted in the front kick panels. The radio is the stock AM.
There's nothing on the FM radio that I want to listen to and I don't want a bunch of CD's cluttering up my ride so this was a great option for me. This system sounds awesome, is cheap, easily hidden, and the ways it can be used are diverse. So that's another option for you.