Finally after about 7 hours I've done it. :D
I've changed the blogging plugin to blogtng and until now it was worth it.
It is easier to manage the posts and blogs although there is IMO the feature missing to create a new blog using the webinterface.
Until now you have to create a new <blog>_entry.php file for each blog you want to have in <dw-dir>/lib/plugins/blogtng/tpl/.
But hey, there isn't a stable version out means I'm using something between alpha and beta here and is fun to use it.
Let's see how this plugin will be developed in future.