If your dash is uncut where the stereo mounts, what ever you do, DO NOT CUT IT!!!! If you have an uncut dash, contact Randy and get one of his center console map pocket adapters, here's a link to the thread:
http://www.78ta.com/HTAF/index.php?topic=37692.0 If your dash radio area is already cut up, you can pickup a generic plate for 1 DIN that has a 3/4" border around it, then cut the shape of your dash opening around the plate, that's what I did for my dash since it was already cut up.
Wiring concerned, you have speaker wiring, power wires, power antenna wire and the antenna. You shouldn't have to worry about the antenna it should plug right in. You may need an extension for it though.
Speaker wiring concerned, if you had a 78' or newer, you could use the existing wiring if it's already wired for rear stereo speakers. 77 and older though, you need to run new speaker wire. The older cars were designed with the speakers grounded to the chassis, and I think the gauge wire was designed for 10 ohm speakers, either is reason enough not to use the wiring. What ever you do, keep the old wiring in tact, just don't use it. The gauge of the wire will be determined by your receiver/speaker combination. Who ever you buy your speakers/receiver from should tell you what gauge wire is recommended. If you're staying under 50 watts per speaker though, most likely 16 gauge speaker wire will do the job.
The factory ran the rear speaker wire down the passenger side under the sill plate (plate under door), then up and around under the 1/4 side panel to the trunk. I would use the same route. One tip, make sure your left and right speaker wires are the same length. Don't be tempted to make the right speaker wire shorter since it doesn't have to run as far.
Someone else can chime in, but someone sells a center speaker adapter that lets you mount two 3.5" speakers in the center speaker location. That's ideal since it prevents you from hacking up door/kick panels and the center console. I think I've seen the adapter in the popular catalogs, Fbodywarehouse may sell them too.
As for the power and antenna wiring, you need to find a "wire harness adapter", that uses the existing radio harness that plugs into your stock radio to splice into an aftermarket receiver's harness. You will want to do this to prevent cutting up wires under your dash. If you can't find a harness adapter for your year, then I would recommend running new wiring from your fuse box to your new CD player to avoid cutting up wires. The speaker wires from the stock harness will not be used since you'll be running your own speaker wires.
If you tap into existing wires under the dash, red wire with black stripe will have power when car is in "run" mode, and orange is what you want for the radio's "clock". Again, I would run a separate wire from the fuse box to the radio for the main receiver power, and maybe even add a fuse inline too.
Some finishing touches would be to add baffles behind your rear 6 x 9 speakers, both to protect your speakers in the trunk and to add a little more base to them. Here's a link to the baffles I used:
http://www.amazon.com/DEI-050380-Boom-Speaker-Baffle/dp/B0039Z3T4C/ref=sr_1_2?ie=UTF8&qid=1354290289&sr=8-2&keywords=6+x+9+baffle+speakerOh and
www.crutchfield.com is your friend. Even if you don't buy the speaker/receiver from them, there's no other better source for car audio in my opinion.
