I just found out about compiz-gtk:
===
OpenGL window and compositing manager - Gtk window decorator
This package contains a window decorator that uses Gtk to provide a look and feel similar to that of the metacity window manager.
So that probably is the gtk-window-decorator I was looking for. However, it depends on Metacity, which is of course not what I want on Xubuntu.
I just found out about compiz-gtk:
===
OpenGL window and compositing manager - Gtk window decorator
This package contains a window decorator that uses Gtk to provide a look and
feel similar to that of the metacity window manager.
===
So that probably is the gtk-window- decorator I was looking for. However, it depends on Metacity, which is of course not what I want on Xubuntu.