Logged In: YES 
user_id=458461

I ran the tests through the IDLE IDE. All tests succeed when
I run regrtest.py from a command prompt or from with Cygwin
1.5.11. (240 tests OK, 50 tests skipped as expected) 

I don't know if running the tests and/or using universal
newlines support within IDLE is/will be supported. Please
close this bug if it's inappropriate.

For more information 
Python is not in the PATH and
TIX_LIBRARY=C:\Python24\tcl\tix8.1 and
TK_LIBRARY=C:\Python24\tcl\tk8.4

From Python shell within IDLE:

>>> import sys
>>> dir(sys.stdin)
['_RPCProxy__attributes', '_RPCProxy__getattributes',
'_RPCProxy__getmethods', '_RPCProxy__methods', '__doc__',
'__getattr__', '__init__', '__module__', 'encoding', 'oid',
'sockio']
>>> print sys.stdin
<idlelib.rpc.RPCProxy instance at 0x00B20508>

From a Python shell run from a command prompt:

>>> import sys
>>> dir(sys.stdin)
['__class__', '__delattr__', '__doc__', '__getattribute__',
'__hash__', '__init__', '__iter__', '__new__', '__reduce__',
'__reduce_ex__', '__repr__', '__setattr__', '__str__',
'close', 'closed', 'encoding', 'fileno', 'flush', 'isatty',
'mode', 'name', 'newlines', 'next', 'read', 'readinto',
'readline', 'readlines', 'seek', 'softspace', 'tell',
'truncate', 'write', 'writelines', 'xreadlines']
>>> print sys.stdin
<open file '<stdin>', mode 'r' at 0x0095E020>

PS: I changed the summary because this problem is IDLE specific.