Coach Mike - totally depends on where your blog is hosted and what blog software is running it.
If it's through blogger.com (blogspot) it's very easy to do. If you are at your blog dashboard (get to it by going to blogger.com and logging in) you'll see a settings link to the right of the "New Post" button, it's two links over. Click that to go to your blog settings.
On the next page the very last link in the header is Permissions. Click that.
On the permissions page there's a button that says "Add Authors". Just enter in the email address of those folks you want to invite.
That's pretty much it.
Now if you're not on blogger.com then you'll have to tell me which host you use. I can probably figure out how to add authors there.
A blog is a great way to get people to read information, but it's really intended just for one or a couple authors and isn't conducive to discussion. You may want to consider ditching the blog in favor of a more social site hosted at ning.com - it's a free community site host that gives you a lot of options for sharing info. There's a blog feature, discussion forums, photo and video gallery capabilities etc. etc. You might want to look into it. I just started with TNT recently and I am considering creating one for the chapter I just joined.
-matt
