Installing a new head unit

Allright, I've read all I could about installing head units from just about any place that I could find. But I seem to completely lack even the most basic of knowledge. I plan on installing a Sony CDX-MP40 into a late 90's Accord in the near future and it will be my HU install. First off, do I need to purchase a new wiring harness for the unit, and will I also need the plastic adapter to make it fit into the dash? And secondly, is there any place online I can go that will basically show me step by step how to install a head unit, and if not, would any of you be willing to basically "hold my hand" throughout the process? You can reach me on AIM at JoeMetal2TheCore or email me at jch9@geneseo.edu . Thanks.

Go to Crutchfield.com.  They'll show you everything you'll need, and they have good and ample info too.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.