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.

IdealAds WordPress Plugin

Take total control over what advertising appears on your site, and where precisely on your site it appears. We provide a database of ads, searchable by Keyword, so that publishers may rapidly track down the the Ideal Ad for any given article. Our unique interface allows publishers to insert multiple ads across multiple paragraphs in a matter of seconds! The IdealAds WordPress Plugin allows WordPress publishers to quickly and easily insert any Ad of their choosing anywhere in their Blog. Monetize your blog like never before. Right now, Amazon Affiliate Ads are the sole category of advertising available in our database. However, the Ad content of our database is set to grow exponentially in the incoming few months. Using the IdealAds plugin could not be any easier. Go to your blog and login. On any page of your blog, toggle Ad Insertion mode by hitting ctrl+x. An option to insert an Ad will appear next to each and every paragraph. Select the paragraph where you would like the Ad to go, and click Insert_Ad. Search our Ad database using the set of keywords that best describes the content of that particle post. A preview of all appropriate ads will be returned in the search results. Select the Ad that you like best and it will instantly appear in your Blog post. Insert multiple Ads across multiple in a single Blog post. Assign multiple Ads to a single paragraph; they will load randomly with the page, and optimize automatically based on click-through-rate. Toggling with ctrl+x