After a long, tedious process (see previous posts), I got 64 bit python, 64 bit tcl/tk, and 64 bit tkinter all to work! I can now use the TkAgg backend in matplotlib! Python 64 bit on Mac OS X: Sam Skillman's post Tcl/Tk 64 bit: a post on the tcl/tk forums tkinter 64 bit: python bug report 4017 (last two posts give the solution) and my posted solution