How do I set up a blog that has multiple blogs (or parent categories) with different styles using WordPress?

I would like to set up a blog similar to or like the Sugar Networks (

They are basically separate blogs on one site (readers can leave comments using the SAME registration across all sites on network).

I currently have one blog up and running using a single wordpress installation. I would like to (like the example websites above) host several blogs or categories on one site (so that users don’t have to register for a different username/password for each blog. I also would like each blog/category to have a unique header and background.

Is there a way to do this using a single installation of wordpress or should I try to figure out how to use WordPress MU?

The easiest possibility I was thinking of:

– Creating "category" pages as the separate blogs (I’m not sure how to customize).

Thanks in advanced!