Assuming you are using the "Mac OS X 64-bit/32-bit x86-64/i386 Installer (2.7.1) for Mac OS X 10.6", note that the download page was updated sometime ago to include the following warning: "[You may not be able to run IDLE or use Tkinter with this installer] and refers you to: 

    http://www.python.org/download/mac/tcltk/

As noted there, there are problems with using IDLE with that installer; the recommended solutions there are to either install the most recent ActiveState Tcl/Tk 8.5.9 and a newer version of the 2.7.x 64-bit/32-bit installer (2.7.2rc1 is currently available, the final 2.7.2 version is expected to be available later in June).

   http://python.org/download/releases/2.7.2/

Or switch to the 32-bit-only 2.7.1 installer for OS X which does not link with the problematic Apple-supplied Tcl/Tk 8.5.

If this does not solve the problems you are seeing, please re-open and supply more information about exactly which Python you are using and the errant behavior.