I just started a new forum again since a long time. I know Floris had a tutorial some time ago to add space between the categories. But i can't find it anymore. Can anyone please help me?

This worked quite well for me. Hope it's OK to post a link?

http://www.vbulletin.org/forum/showthread.php?t=123713&highlight=default+forum+seperate+categories

Accually its right here. Was just reading this hack and then saw your post :P

Link -> http://www.vbulletin-styles.com/showthread.php?t=5688&highlight=moderator