Conditional is_loggedin tag?

I really need a conditional tag which I can use to see if the page viewer is logged in or not. Ideally, it would have the following semantics:

int userlevel = is_loggedin();

with the unfortunate side effect that not logged in users and level-0 users both return 0. This would allow boolean tests to see if a user was logged in or not and display different content based on this.

I would also like a function called “get_userlevel()” with these semantics:

int userlevel = get_userlevel()

and returns the user level from 0-10 or “-1” for not logged in.

Does this functionality already exist under some other name?

Is there some good plugin or way to handle user groups? I’m considering Multiply, but that looks like it actually has different blogs for the different groups.

I am really looking at WordPress as an easy to administer CMS, rather than a blog site.