lenherr, workspaces are the solution for what you are looking for, within Tiki.
You need to learn how to configure them (read the English documentation through http://edu.tikiwiki.org )
In short, you need to setup a structure module at the workspace desktop of the workspace you like (each workspace has a group created with permissions from a template assigned to them, different from the perms. of other workspaces).
To install that feature, you need to install AulaWiki Mod (latest by the time of this post is v1.2). See edu.tw.o to learn how to install it.
HTH, and consider joining us at edu.tw.o is you like workspaces feature!