Python try…except comma vs ‘as’ in except

What is the difference between ‘,’ and ‘as’ in except statements, eg:

try:
    pass
except Exception, exception:
    pass

and:

try:
    pass
except Exception as exception:
    pass

Is the second syntax legal in 2.6? It works in CPython 2.6 on Windows but the 2.5 interpreter in cygwin complains that it is invalid.

If they are both valid in 2.6 which should I use?