I've just installed Python 2.6 on Mac OS X 10.5.5 and IDLE won't start.
IDLE 2.5 still works fine.

Here's the traceback:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/Current/bin/idle",
line 3, in <module>
    from idlelib.PyShell import main
  File
"/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/idlelib/PyShell.py",
line 14, in <module>
    import macosxSupport
  File
"/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/idlelib/macosxSupport.py",
line 6, in <module>
    import Tkinter
  File
"/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/lib-tk/Tkinter.py",
line 39, in <module>
    import _tkinter # If this fails your Python may not be configured for Tk
ImportError:
dlopen(/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/lib-dynload/_tkinter.so,
2): Library not loaded: /Library/Frameworks/Tcl.framework/Versions/8.5/Tcl
  Referenced from:
/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/lib-dynload/_tkinter.so
  Reason: image not found