top-level window position/size questions

[Vadim Zeitlin <zeitlin dptmaths ens-cachan fr>]

 Hello all,

 I've got two, hopefully simple, quetions. Unfortunately, I couldn't
find the answer reading documentation and sources, so I'd like to ask
for your help.

 1) how can I get the position of the main program window?
 2) how can I set the min/max-imal size for the main window, i.e. prevent
    user from shrinking it to 5x5 pixels?

 Thanks in advance!
VZ