Tkinter radiobutton problem

I'm writing a simulation program using PythonCE and Tkinter.

One of my dialogs has a group of radiobuttons. On my Linux box, these
are rendered correctly, but on PythonCE they display as checkboxes.
They behave like radiobuttons - when one is activated, the others are
de-activated, but they look like checkboxes. The program works OK, but
it looks a bit unprofessional. Has anyone had a similar problem and does
anyone know how to get the radiobuttons to be rendered correctly?

I'm using an iPAQ 5550 with Windows Mobile 2003.

Andrew Booth