hey v@ano, thanks for helping me.
here we go:
<code>
ErrorDocument 404 /404.html
RewriteEngine On
RewriteCond %{HTTP_HOST} ^mysite\.de$ [NC]
RewriteRule ^(.*)$
http://www.mysite.de/$1 [L,R=301]
#RewriteBase /is/xxxx/xxxx
RewriteRule ^lightbox\.htm$ lightbox.php?%{QUERY_STRING}
RewriteRule ^lightbox\.([0-9]+)\.htm$ lightbox.php?page=$1&%{QUERY_STRING}
RewriteRule ^search\.htm$ search.php?%{QUERY_STRING}
RewriteRule ^search\.([0-9]+)\.htm$ search.php?page=$1&%{QUERY_STRING}
RewriteRule ^cat\.htm$ categories.php?%{QUERY_STRING}
RewriteRule ^cat([0-9]+)\.([0-9]+)\.htm$ categories.php?cat_id=$1&page=$2&%{QUERY_STRING}
RewriteRule ^cat([0-9]+)\.htm$ categories.php?cat_id=$1&%{QUERY_STRING}
RewriteRule ^img([0-9]+)\.htm$ details.php?image_id=$1&%{QUERY_STRING}
RewriteRule ^img([0-9]+)\.([a-zA-Z0-9]+)\.htm$ details.php?image_id=$1&mode=$2&%{QUERY_STRING}
RewriteRule ^postcard([a-zA-Z0-9]+)\.htm$ postcards.php?postcard_id=$1&%{QUERY_STRING}
RewriteRule ^postcard\.img([0-9]+)\.htm$ postcards.php?image_id=$1&%{QUERY_STRING}
RewriteRule ^([a-zA-Z0-9_-]+)\.htm$ index.php?template=$1&%{QUERY_STRING}
RewriteRule ^sitemap.xml$ google.php
</code>