Newbie doing lengthy initialization with Tkinter gui

[Pasi Oja-Nisula]

I have written a small image viewer application for
sorting out photos downloaded from camera. This was quite easy,
thanks to the great Python Imaging Library. Since the loading and 
thumbnailing phase takes a while at the start of the program, 
I figured that it would be nice to show the gui and put some kind
of "loading image 25/50" text there while processing the images. 
So now I construct the simple Tkinter gui in init and when mainloop 
is called the gui is shown.

The question is how (or where) can I call my loadImages function right 
after the mainloop starts? Or is there a better way to do this?

Pasi