If you have already created a blog, or are thinking of one, you may find yourself covering a couple of topics you really want to separate into two blogs on your single site. They may just be different enough, but not so unrelated that they each deserve their own blog and WordPress installation.
This is actually very simple, when using categories and your custom menus in WordPress. You can categorize certain posts and create buttons in your navigation bar to give your readers the illusion that they are two separate blogs. Watch this video tutorial that will show you how in just a few steps.
NOTE: One thing I did not mention in this video, when you create these two separate blogs, you can also easily separate all categories assigned to each on in a menu in your sidebar using the menu feature and the custom menu widget.
You may also be interested in my tutorial on Creating Your Navigation Menus in WordPress.