There is nothing really special about doorway pages, except they are specifically designed to have the right number of words and keywords, and in the proper places, to rank well on the search engines. Good doorway pages blend into the whole site and provide you with links and informational text just like any other page, except they are designed to be found when you need them. Well designed doorways have graphics and good layout. You might not notice them unless you know how to look. With some java-redirects you will pass through the doorway before you notice it, unless you keep your eyes firmly fixed on the status bar.
Many marketers do make special pages for all related keywords for each major search engine.
However be careful not to create too many of them or you risk becoming a spammer. No, not one who eats luncheon meat. Some despicable spammers create thousands of pages in order to flood the search engine with their pages, and give marketers a bad reputation. Avoid the temptation. Another domain had 2.5 million pages indexed by another search engine using up a sizeable portion of the engine's database.