If I have 2 domains, altoonadesign.com and programming-perils.com that are both pointed to the same server.
How can I make programming-perils site root the blog
folder on the real site root. and disallow access to the blog
folder from altoonadesign.com using .htaccess?
I'm going to make a leap and assume you're using Apache. You'll want to set up separate VirtualHost blocks for each site (or different site files each containing a virtualhost block, however you're comfortable), and set them to have different DocumentRoots.
A better option (so you don't need the /blog in place) may be to move the blog files outside of the tree that contains the other site.