Accessability/Security In A Multi-user Env.

I need to implement some type of security on my database to limit the forms/reports users can access. When implemented it will be a split database on a network. I'd like to set it up so only certain users can edit/add data on certain forms. Also I want to have more than one user be able to edit/add data at the same time. I'm confused as what I need to do to set up this type of security. I found another post on this forum by Oldsoftboss (Dave) that gave a good, working example of a database with user login screens and different user security levels. My questions are:

1. Can I use his system in place of the built-in Access security?
2 . Do I need to implement both? If I don't use or change the access rights in
Access security, won't everybody be logging in with "Admin" rights?
3. What do I need to do to let multiple users work in the database at the same
time? I've already changed the database to "shared".
4. I don't want the users being able to change the forms, queries or reports
so I'm distributing an MDE file. Is there anything else I need to do so
users can't access the "design" button?

Needless to say, this whole security thing confuses me. Any help would be appreciated.

Rod