OK, I just found the fix – within two minutes of my last email to you (after spending 6 hours on it)!!
I needed to use the following variant for the macports installation (like I said, I rather new at the Mac and unix):
sudo port install py26-matplotlib @1.0.1 +gtk2
for the matplotlib installation. it works now, although I still get this message:
Xlib: extension “RANDR” missing on display “/tmp/launch-KDlxaE/org.x:0”.