Thema: Problem with installing Joomla and components on strato . de

Hello, excuse me for using English, but I'm not from Germany.

I am making a website based on Joomla for my german friend who has a hosting in strato . de

I encountered many problems with installing Joomla on this hosting. After uploading Joomla 1.5.23 files on their server and trying to install Joomla, I got anerror:

Code:

Warning: file_put_contents(.../configuration.php) [function.file-put-contents]: failed to open stream: Permission denied in /.../installation/installer/models/model.php on line 850

After this, I created manually configuration.php and filled it with database data (passwords etc).

Joomla seemed to be installed, but when I tried to install any extension, I can't do it since it shows only errors like:

Code:

Cound not create directory
Component install: failed to create directory

Of course I tried to change directory permissions to 777 but it didn't help, always the same problem and no availability to install any component.

I also tried to install Joomla via strato own installator, but it gives the same errors.
I contacted strato de help office, but they answer was "we do not offer any technical / scripting support for either of the 3rd party CMS's".

Could someone help me please with that?
Has anyone succeed with installing Joomla and components on this hosting?

I would appreciate any help.