How to get WordPress Blog into a separate URL?

I want to have 2 or 3 different wordpress based blogs hosted under one account. I already have several domain names and a host and have already installed WP blogs into separate folders through FTP.

But, what I need to know how to have the domain URL point straight to the blog without having to move files into the root directory. If domain name is 123blog.com, i want it to go straight to the Blog instead of having 123blog.com/blog/ in the URL.