I retired June 30, 2007. Before I bailed, I started meeting with Small Business Development Center (most are hosted by community colleges -- at least in CA) counselors who provide free consulting. I put in ten to twenty hours of research on my own for every hour with them, but they helped guide my thinking.
Because of the ease, I started a sole proprietorship. I filed an SS-4 with IRS (online on a Sunday) to get an Employer Indentification Number, filed ficticious name form with Monterey County (I live in unicorporated area), and ordered business cards.
I was advised by one counselor to form an LLC and advised by an accountant to form an S corporation -- which is what I probably will probably do January 1.
I can personally recommend SBDC counselors.
There are also a number good sites and books available -- particulalry
http://www.nolo.com/