1. I want this
http://www.mysite.com - one static page with links to subfolders (or sub domains)
http://www.mysite.com/site3/ and so on if needed
Every site site1, site2, must be WordPress installation but the main idea is to have one database for the admin and users (cause I intend to integrate it with phpbb3) and different table prefixes (if needed) for the content of every site.
And also i want to have different templates and so on on every site but to keep the easy way to update WordPress with new versions.
I've read about the different multiple installation methods, but i'm a bit confused which will be the best for may situation. So i'm waiting for your suggestions.