Well BrowserUK pointed out the limitations of using threads with Tk. The threads must be created before any Tk statements are made, to prevent copies of the Tk widgets getting into the threads, and causing confusion. That is why they say, that "Tk is not thread-safe". It can be used with threads, but not without precautions.

I will point out, that the Gtk2 thread model will allow you to do what you want, with it's "thread-safe" mode. You need a recent version of Gtk2, and look at it's thread_usage.pl in the examples directory.