I have my site up and running.  Guest have to register similar to this site to use the forum, etc.  The problem is anytime they log in they are given the ability to edit the sites content.  I went through settings and changed it so that anyone who is not admin should be denied this function yet it continues to happen.  What would be the cause of this?

What versio of DNN are you running?  Can you elaborate on "they are given the ability to edit the site's content"; are you talking about a specific module or does it look like they have full administrator right or somewhere in between? Find a recently registered user, make note of what Roles they are in.  Then go to the page where they can edit things and examine the page settings and then each module's settings and make sure none of the Roles that the user is in are checked for Edit (Page or Module).  Also, have you logged in as one of those users?  Can they actually make a change or does save/update post and forget the changes?