Sorry, I was not clear.
With python 2.5.2, "import nul" correctly raises ImportError, even if
the error message is slightly misleading.

With a recent release25-maint (and all other branches), "import nul"
does succeed, and creates an empty module. 
"import con" seems to block, it actually waits for the user to enter
text and type ^Z. Then it prints to the console some bizarre text that
looks like the content of a .pyc file:

Python 2.5.3a0 (release25-maint, Jun 11 2008, 13:17:36) [MSC v.1200 32
bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import con
^Z
a=1
b=2
c=3
^Z
│≥
    c        ☺   @   s►   d  Z  d☺ Z☺ d☻ S(♥   i☻   i♥   N(☻   t☺   bt☺
  c(    (    (    s♠   con.py   <module>☺   s☻   ♠☺    [27520 refs]
>>> dir(con)
['__builtins__', '__doc__', '__file__', '__name__', 'b', 'c']
[27533 refs]