IDLE and Tk 8.5 don't well work together for both Python 2.5 and 2.6a
(SVN version).  The reasons are related but different.

In Python 2.5, you can't select any text in the IDLE window and whenever
a calltip is to appear, you get a backtrace ending with "invalid literal
for int() with base 10: '(72,'".  That comes from an interaction between
WidgetRedirector's dispatch function and _tkinter.  The Text widget's
bbox method returns a tuple of ints, the dispatch function isn't
monitoring bbox, so it returns the tuple as is to _tkinter, where
PythonCmd converts the tuple to a Python string, not a Tcl list, so when
Tkinter sees the string, it can't convert to a tuple.

The Python "2.6a2" SVN version of _tkinter fixes that bug but exposes
others (Ikinter.py, tupleobject.c), so I've attached a simple patch for
Python 2.5.  The SVN version of idle appears to work, so this patch
should only be on the 2.5 branch.