I replaced mine a couple of years ago and remember it taking a lot of force to loosen the pulley. It was tricky holding the (relatively small) wrench in one direction while applying a lot of force with a larger breaker bar in the other direction. I was able to do it, so it is definitely possible.
Best of luck and let us know how it turns out.
ddb
http://986forum.com/forums/performance-technical-chat/21779-clicking-noise-solved-alternator-pulley.html