I've installed Python 3.1.1 on OSX today.
1) When I use the Japanese input from OSX, IDLE interprets any character 
I attempt to type as a space.
2) When I paste a Japanese string from a different place, it is 
correctly handled. For ex:
>>> print('ここ')
ここ
>>> 

While on Python 2.5's IDLE I had:
>>> print('ここ')
Unsupported characters in input

>>> 

by default.

In any case, IDLE 3.1.1 does not respect the input source and that makes 
it impossible to directly type Japanese (if not other double byte 
character based languages).

Note: IDLE respect OSX dead keys and I can correctly use "Alt+c" to 
input "ç".