With the autoblog plugin this is possible

I reviewed AutoBlog Solution and description.

Description: This plugin creates a new blog when someone registers on b2evolution. For every registration a new blog and the corresponding category in the blog will be created. Blog short name and category will have the same name as login.

We only have 1 Main Blog at this point. We would just like to automate a way for users to signup for membership and then be able to post an article to blog vs. comment.

This doesn't seem at face value to be the solution. Or is it?

You can give a set of generic permissions to one of your groups, then declare that as the group that newly registered people will be in. For example on your App settings->General tab you say that new bloggers are in the "Basic Users" group and are level 1. You then use your Blog settings tab to pick a blog, and on the Group permissions sub-tab you define what permissions the Basic Users group has.

Be aware that b2evolution is, by design, a collaborative application. That means that anyone who can post and edit in blog #N will be able to edit the posts of anyone else in blog #N. That bugs a lot of people, but it is what it is. I guess you have to know and trust your bloggers to not be rude.