[pygtk] Centering widgets horizontally on screen

[Art Hunkins]

Another newbee question (or two):

I've no problem centering text in the middle of the screen, but otherwise 
don't know how to do the same with buttons and Hboxes. Hence:

1) how to center a group of 4 buttons horizontally?

2) how to center a nested (packed) set of boxes horizontally?

I assume gtk.Window and gtk.WIN_POS_CENTER are involved, but that's about 
all I "know."

Art Hunkins