Sorry to be obscure, Ronald. I mistook my configuration problem, described below for the original problem. But I can reproduce the problem with opening an existing file under IDLE, which is a segmentation fault. When opening a new window, I get a blank screen but no >>> prompt.

I should have done this before on my two boxes. It shows pretty clearly that the abort trap problem in 2.6.x is my configuration problem. On the development box, I have mutliple Pythons, with varying degrees of IDLE success; on the production box I have only the factory installed 2.6.1 with no IDLE problem other than the one originally reported. Both boxes are under 10.6.4.

Development:
Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
$ /usr/bin/idle2.6
CGColor with 1 components
Abort trap
# This is probably due to paths crossed with 2.6.6
$ sudo /usr/bin/idle2.6
2010-10-20 10:12:16.329 Python[11954:1707] __CFServiceControllerBeginPBSLoadForLocalizations timed out while talking to pbs
2010-10-20 10:12:31.868 Python[11954:1707] __CFServiceControllerBeginPBSLoadForLocalizations timed out while talking to pbs
0
#IDLE works, otherwise, except for the segmentation issue

Production:
Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29) 
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
#IDLE works, except for the segmentation issue

for completeness:

Development:
Python 3.1.2 (r312:79360M, Mar 24 2010, 01:33:18) 
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
$ idle3
Floating point exception

Development:
Python 2.7 (r27:82508, Jul  3 2010, 21:12:11) 
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
** IDLE can't import Tkinter.  Your Python may not be configured for Tk. **

Development:
Python 2.6.6 (r266:84292, Aug 28 2010, 10:17:47) 
[GCC 4.2.1 (Apple Inc. build 5664)] on darwin
#IDLE hangs