I'm new to Python and am presumably making a basic error, but this has had me occupied all afternoon and evening trying to google an answer without success. Please help

I've copied a simple program from the web to put a window up on the screen. The first line is "Import pygtk". When I run it it returns "Import Error: No module named pygtk".
I've also tried this interactively in LXTerminal - same result. And the same thing happens with "Import gtk".
Do I need to do something first to install these modules ? I thought it was part of the standard Python install....?
Thanks for any help.
Regards,
David L.