Documentation for IDLE states:

    Starting IDLE on UNIX 
    On Unix, just type "idle" at a command prompt. This should bring
    up a Window similar to the one above. (If it doesn't, look for
    the "idle" script in the Tools/idle directory in the Python source
    distribution.)

http://www.python.org/idle/doc/idlemain.html

I believe that is obsolete, I cannot see a Tools/idle directory in 
either 2.5 or 2.6. Perhaps better instructions might be:

    (If it doesn't, run "python LOC/idlelib/idle.py" where LOC 
    is the location of your Python source distribution, usually 
    /usr/lib/python*.)

or similar.