alternator nut?

[Chuck Ciaffone <chuckc@ibm.net>]

Just tried to pull the alternator pulley in preparation
for replacing it. Clamped the case in a vise, stuck a
bar in thru the fins to lock the shaft, then tried to
loosen the nut (counter clockwise?). The wrench turned.
The nut turned. I think the whole #$@% shaft turned.

How do I get the bugger off?

chuck