If you're just want to create an admin login, you only need SecurityAssist. If, however, you want your admin section to contain Insert and Update pages with an HTML editor (for WYSIWYG editing), then you need iRite as well. If you're unfamiliar with building admin pages, you might also consider DataAssist. But, if you're going the full route with those 3, you should take a look at the Web Developer Suite.
Didn't mean to go all sale-sy on you. It's just that there are a lot of variations to choose from depending on your skill set and what you're trying to accomplish.
Best - Joe