Can multi-site do: site1.com/blog & site2.com/blog ?

Hi All,
I’ve read a ton of tutorials on setting up a multi-domain, or multi directory version of WP 3. But I haven’t found anything regarding setting up WP on a single server to allow a single WP 3 install to house a multi domain & sub directory system.

Is it possible?

So for example: http://site1.com/blog & http://site2.com/blog & http://site3.com/blog

Thoughts?