Hi Gernot,
Well you'll have to be prepared to learn something
Luckily tcl/tk is very simple.
Look at the centre.tcl file in the plugins folder - that's what gets run when you select the centre plugin from the tools menu (provided you have the plugin pack installed).
Also, look at Frank's tcl file for the direct X export plugin.
And, have a look in the tcl folder - that's where AC3D's UI is defined.
If you have any questions, ask here.
Andy