Sorry I made a mistake in my previous patch (_LARGEFILES instead of _LARGE_FILES).

Here is a better one:

Index: configure.in
===================================================================
--- configure.in	(révision 88395)
+++ configure.in	(copie de travail)
@@ -1376,6 +1376,14 @@
 if test "$use_lfs" = "yes"; then
 # Two defines needed to enable largefile support on various platforms
 # These may affect some typedefs
+    case $ac_sys_system/$ac_sys_release in
+    AIX*)
+        AC_DEFINE(_LARGE_FILES, 1, 
+        [This must be defined on AIX systems to enable large file support.])
+	;;
+    *)
+        ;;
+    esac
 AC_DEFINE(_LARGEFILE_SOURCE, 1, 
 [This must be defined on some systems to enable large file support.])
 AC_DEFINE(_FILE_OFFSET_BITS, 64,

The test fails in a different way now:


======================================================================
ERROR: test_large_file_ops (__main__.CIOTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./Lib/test/test_io.py", line 418, in test_large_file_ops
    self.large_file_ops(f)
  File "./Lib/test/test_io.py", line 323, in large_file_ops
    self.assertEqual(f.write(b"xxx"), 3)
IOError: [Errno 27] File too large

======================================================================
ERROR: test_large_file_ops (__main__.PyIOTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./Lib/test/test_io.py", line 418, in test_large_file_ops
    self.large_file_ops(f)
  File "./Lib/test/test_io.py", line 323, in large_file_ops
    self.assertEqual(f.write(b"xxx"), 3)
IOError: [Errno 27] File too large

----------------------------------------------------------------------
Ran 395 tests in 27.958s


Here is your trace:
phenix:~/.buildbot/python-aix6/3.x.phenix.xlc/build\> ./python 
Python 3.2rc2+ (py3k:88393M, Feb 11 2011, 14:56:34) [C] on aix6
Type "help", "copyright", "credits" or "license" for more information.
>>> f = open('foo', 'wb')
[55983 refs]
>>> f.seek(2**32)
4294967296
[55987 refs]
>>> f = open('foo', 'wb')
__main__:1: ResourceWarning: unclosed file <_io.BufferedWriter name='foo'>
[55994 refs]
>>> f.truncate(2**32)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 27] File too large
[56027 refs]