Yup. It's in one of the files in the conf folder. I always forget which one but there are only a few so it shouldn't be too hard to find it. I think in older versions you would actually change each table's prefix, but I could be wrong. It might be a variable all the way back to the beginning of time. But anyway yeah you can do that by editing a file in the conf folder.

Hi.
I did it. First I had to chance -advance in conf-dir. and so I went to database via phpmyadmin an rename the table one by one. mark the table and click on "operations" there you have different choises.
My english is not so god but I hope you understand me.

Just run the installer for your second blog installation and it'll make the tables with the proper prefix.

I gotta back up though. Do you mean two completely different blogs with two completely different admin passwords, or just two blogs that the same admin (or other users) can post in? Either is possible. The first requires the second set of tables. The second is already a normal part of one b2evolution installation.

"Do you mean two completely different blogs with two completely different admin passwords,"

yes. that is wath I want to do. I will tri to do this later to day.
I have to run now. (have familie :D waiting)