My forum (relative) path is "../cgi-bin/forum".
I know it's ok because I get an error (telling the old db was not found) when I enter anything else, so this is the correct path.
My prefix in the origin database (in MySQL) is "phpbb_" (I'm sure), so I entered this.
When I click the "Begin conversion" button, I get this error:
The convertor was not able to find tables with the specified prefix. Please make sure you have the old within the same database as your phpBB 3.0.x installation. The default table prefix for phpBB 2.0.x is phpbb_
I know I won't get support for this by now. I just wanted to see the second screen in action here (not in a snapshot by others).