I recently upgraded from python 2.3 to 2.5. But idle doesn't launch
anymore, either with right-clicking a .py program an doing "edit with
IDLE" or with launching the idle.py file itself. 
When I launch idle with the command line, it gives the following error
several times:

Warning : configHandler.py - IdleConf.GetThemeDict- 
problem retrieving theme element 'buitlin-foreground'
from theme 'vert theme'
returning default value: '#000000'

Warning : configHandler.py - IdleConf.GetThemeDict- 
problem retrieving theme element 'buitlin-background'
from theme 'vert theme'
returning default value: '#ffffff'

"buitlin"? Is is a typo while copying the error message?

The warnings are normal, these theme elements were added later. They
will disappear when you save the theme again.

Now, idle starts another process to interpret the commands, and use
sockets to communicate between them. You may have a firewall problem.

Can you try to run idle.py with the "-n" option? This does not create a
subprocess, all commands are run in the main process.

it's not "buitlin" but "builtin" of course.

idle launches when I use the command line, with or without "-n", but I'm
still unable to lauch it normally (by the right click or by the windows
menu ("Démarrer/Programmes/Python25/idle")).
Before, I used python 2.3 and it worked well. I uninstalled and
installed again python 2.5 several times but I still got the same
problem.. it isn't practical at all to lauch idle by the command line!
So I hope you'll have an idea to solve my problem...

I reproduced the problem.
- "python.exe idle.py"  works (with many warnings)
- "pythonw.exe idle.py" fails

pythonw.exe is a Windows (i.e. not a console) application, so sys.stderr
points to an invalid file descriptor; printing lot of warnings raises an
exception when the file tries to flush()...

As an immediate workaround, you may delete everything in the directory named
  c:/Documents and Settings/%USERNAME%/.idlerc
or if you feel it, add the missing entries in the file config-highlight.cfg.

I'll try to correct this problem for python2.5: replace 
   sys.stderr.write(warning) 
with
   try:
      sys.stderr.write(warning) 
   except IOError:
      pass

ok, deleting the contents of .idlerc seems to work fine.
Thank you!

Committed r62448 & r62449.
Thanks for the report!