To run egg-texture-cards, go into your command line and go to the folder where your textures are. Type the following:
egg-texture-cards -p (height,width) -o <final_filename>.egg <texture1>.<filetype> <texture2>.<filetype> <texture3>.<filetype>
Then in your script:
buttModel = loader.loadModel("models/interface/fullscreen.egg")
button = DirectButton(geom = (buttModel.find('**/<texture1>'),
buttModel.find('**/<texture2>'),
buttModel.find('**/<texture3>')),scale=0.5)
The height and width ought to be the same number or you will get horrible stretching.