Well take it from someone who use to install stereos for a living and still does on the weekends, IT's AS EASY AS WIPING YOUR OWN ASS.
Those idiots that told you it was a special install were trying to get some extra cash out of you because you didn't know. If all you are adding is the head unit (cd player part) then you'll want to look at something mechanical. The best brand that comes to mind in SANSUI, but if you have the cash and don't mind spending it go for the top of the line digital unit (sony, kenwood, but not pioneer. They seem to be afraid of a little dust).
By mechanical I mean that you have to physically slide the cd into the hole and the push it the rest of the way until it clicks in, much like the old tape decks but for CD applications.
Now as for installation, if you buy a CD player in the box should be a metal mounting bracket that will be used to stop your CD player sliding in and out of the hole(in the hanging dash box). Now all you have to do is trim the original plastic piece (which clips into the front of the box) using a jigsaw until your metal bracket will slide through the hole. Once you have the hole just big enough for the bracket to slide into we can move onto installing the actual CD unit. (make sure the hole and bracket make a really, really tight fit. You don't want the sucker sliding out into your lap when you climb a decent hill).
Take the trimmed plastic piece (some have a cigerette lighter hole in it) decide what side you want the cigerette lighter to be on and then fit your metal bracket(one end of the bracket will have a lip on it, that will need to be on the front side of the pastic piece. To do this hold the plastic piece and push the other end of the bracket through the trimmed hole from the front side to the back side). Next slide the CD player into the metal bracket until you hear it click in. You should notice that on the metal bracket that at the end closest to the plastic, that there should be a number of tabs you can bend up (using a flat head screw driver). Pop up only the ones that will help hold the plastic to the bracket.
now all you have to do is push the CD unit, which is attached to the plastic, back into the hanging dash box (from the back of it) and clip the plastic bit into place. All CD units should also come with a metal strip with a whole heap of holes in it. Find the center one and the retainer screw (supplied usually) and screw this into the back of the CD unit (where the wires go). next bend the metal strip over nice and tight and use two small screws to attach it to the plastic box. Now your CD player shouldn't move an inch. if it does, get an old or new car cleaning sponge and cut it into blocks and wedge them above and below the CD unit between it and the platic box (cushions the impact of big bumps).
Now your unit should be all installed and ready for wiring. If you would like pictures send me a private message with your email and I'll email you some detailed pictures of what I am on about.
the best CD unit I have found over the past 5yrs is SANSUI (especially if you do a lot of rigged 4x4), I have one of them pumping out 4x35w with 2 45w pre-outs. on the front harness I have a 4-channel 240w amp which then splits into 6" phillips splits with dual 3" tweeters (all waterproof and on their own private cross-over networks) then in a custom box behind the front seats I have two 12" phillips competition subs with co-dependant mid range and tweeter seaters. then on either side of them in the same box I have SANSUI competition 6x9" 3-ways. All of the rear speakers are being powered by a 4-channel 800w competition amp. All wiring and speakers etc etc is waterproof. Even the head unit (except it doesn't like salt water, burnt one out the other weekend
beleive it or not I have all of this running of a standard battery and alternator. I get more volume and clearer sound out of my $900 Australian, then most of the wankers around that have spent $1500
Shop around and buy the bits yourself, you'll do a better deal, get the sound you want and build it all at your own pace. Need any help drop me a line.
1.6 22R off it's rocker
"If it's too hard or you're a pussy, give me a go at it"