Try this :

# PHP SECURITY:
<IfModule mod_php4.c>
	php_flag register_globals off
</IfModule>
<IfModule mod_php5.c>
	php_flag register_globals off
</IfModule>

# DEFAULT DOCUMENT TO DISPLAY:
<IfModule mod_dir.c>
	DirectoryIndex index.php index.html
</IfModule>

RewriteEngine On
Options +FollowSymLinks

# prevent duplicate content issues, redirect non-www to www
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule (.*) http://www.domain.net/$1 [R=301,L]

# send all others to b2evolution
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule .* /index.php [L]

¥

doesn´t work...

Fehler: Umleitungsfehler

Die aufgerufene Website leitet die Anfrage so um, dass sie nie beendet werden kann.

same error as all tries before...

By any chance do you have www redirected to non-www in your cpanel ?

You should be able to tell by doing the reverse :

# PHP SECURITY:
<IfModule mod_php4.c>
   php_flag register_globals off
</IfModule>
<IfModule mod_php5.c>
   php_flag register_globals off
</IfModule>

# DEFAULT DOCUMENT TO DISPLAY:
<IfModule mod_dir.c>
   DirectoryIndex index.php index.html
</IfModule>

RewriteEngine On
Options +FollowSymLinks

# prevent dupliacte content issues, redirect www to non-www
RewriteCond %{HTTP_HOST} ^www\.(.*)$
RewriteRule (.*) http://%1/$1 [R=301,L]

¥

this time I got a 404 error... :(

Any chance of a link to where this is happening?

¥