As usual, I'm trying to post a form to a site, but it does it through AJAX. Everything I've tried so far does not work.

First off C, I need to question your intentions here: you don't POST a form via ajax - you can send a ajax request with a post-type message, but not post a form... is this what you mean?
Second - are you using the AjaxRequestor class in the javascript repository or are you just doing this by hand?
Here's the pieces of the header that look suspect to me when I POST successfully from my browser:
Accept: text/javascript, text/html, application/xml, text/xml, */*
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: close
X-Requested-With: XMLHttpRequest
X-Prototype-Version: 1.5.0_rc0
Content-Type: application/x-www-form-urlencoded
Doesn't look bad to me except that there's no content or content size after those headers...
Here's the pieces of the header that look When I try to do it my "traditional" way it just comes back and says that I need a JavaScript enabled browser to submit the form.
Who "says" that? Is it IE/your browser giving that message? Is PHP actually creating that message and sending it back? Need considerably more snippets and such to make heads or tails of this...
/p