I came across a cool plugin that is really easy to use when you want something in your menu or navigation to point to another URL instead of a page within your site.
Page Links To allows you to point WordPress pages or posts to a URL of your choosing. Good for setting up navigational links to non-WP sections of your site or to off-site resources.
After installing and activating your plugin, just go to the page you want to edit and scroll down to the bottom of the page. Just fill out the form show below to tell it where you want that page to point.
Get the Page Links To Plugin here. Let me know if this helps with your WordPress Blog.