Change Tkinter Look and Feel?

[Martin]

Anybody know how to change the menu button that is displayed by the
Tkinter Menubutton and the (derived from it) OptionMenu classes? I
think it must be something from the Motif look and feel which doesn't
fit with my appl which is designed primarily for running on Windows
and OS X.

The default button visual that appears is basically a small rectangle
drawn in relief inside a larger one. I'd like to replace this with a
downward pointing arrow to indicate the drop-down menu.

I tried configuring the the OptionMenu widget with the 'image' keyword
to be, but that only resulted in the image appearing next to the
default one for the button instead replacing it. Is the look of this
button hardcoded in the tk or tcl libraries themselves?

The Pmw module has the same problem since it's using the standard
Tkinter widgets internally.

Best regards,
-Martin