If you’re fairly well-versed in WordPress plugin development, you could write a couple plugins, one to create your users with wp_create_user(), and another to insert your articles as Posts using wp_insert_post() (which, among other things, allows you to specify the post_author on each post that you insert).
If you’re not so comfortable writing plugins, then there are a couple of tools that might make your life easier. One is Import Users from CSV — I’ve never used this plugin, but it sounds like something that might work for you. Once you’ve got your users created, WordPress has some import tools built in to the backend at Tools > Import. If you can craft an RSS feed for your existing articles — or if you’ve already got one — you can import your articles using the RSS importer.
If that doesn’t work out for you, there are a host of “importer” plugins to try. My only recommendation is to backup your database before you try any of them.
Edited to Add — there’s a Codex page on importing content — it may answer some questions for you.