I would like to have my blog work like this. When they go to my site the blog will appear with no posts visible. Where the post would normally be there will be 1 posts that basically will tell them to register to view the blog, and all the other links that will be in my site. (Forum, Photo Gallery, etc) Basically I want to make sure only people that register for my site are able to view what’s inside. I know how to change the links in the left column but I do not know how to make the post appear and disapear. How do I do this?

What you would do is put a hard linked entry on your index (using entry_id parameter) and then restrict access to all other templates to only the proper member groups.  Well, not all other templates - you’d leave have to make sure tha the registration and login forms remained available, of course.  Then just include a link for those members in your index.  You could even include the login form on the front page for those people that are registered, or do some conditional redirecting if they’re logged in, etc.