I have directadmin + mod_ruid2
When I install joomla 1.5, I have a message at the end, writing configuration.php is not writeable (chmod 644).
This file has been writed with my option, so I suppose it is just a problem at the end of installation.
I chmod to 666 then reinstall, and no problem.
At the end of installation, configuration.php is set back to 644
But there are a lot of directory in 777 (they have to be 755 with mod_ruid)
Note, when I install joomla 1.7 on the same server, there is no problem. I do not check for chmod.