I didn't see anything about getting payment setup. I know it's different for everyone, so that may prove difficult... but maybe even just walking through setting up the Credit Card module / encryption settings and using the Test Gateway for running through test checkouts. From there it's fairly simple to plug in a more specific gateway module. I wrote a tutorial on this, but it doesn't quite cover encryption settings setup - that still trips people up.
Thanks Ryan. I'm afraid we're woefully unqualified to write such a thing, and I think that would belong more with more of a functional setup guide, rather than visual/workflow/usability stuff. But since we're covering the meta level of accepting payments on your site, I'll see if we can get in something about the test gateway.