Multiple Blog On One Page With Multiple Tabs

Hi All,

I am going to set up a new blog using WP, but before I do I would like to get your feedback on what is the best and easiest approach.

I will have single host with single admin. Here is what I want:

* A main page with multiple tabs to multiple blogs. For example, the main page has three tabs: topic1, topic2, topic3. The topic1 is the default blog. When topic2 or topic3 is clicked, it would take the user to the specific blogs, mind you not pages. Each blogs will have its pages.
* Each blog will have their independent theme and style.
* I would like to have a single database.
* If possible, single install on WP.

The question what is the easiest way to do this?
• Multiple install of WP on a single DB
• Use category but single install of WP on a single DB

I want only a few blogs, say 3 or 4. Not a whole lot. So want to avoid MU.

Are there some ready made themes for this kind of main page? Any pointer with some example would help a lot.

Hope this is an easy question, and many people have already done it. Thank you for your help in advance.