If you don't have any success using the starter motor method above (which I haven't tried myself) - here is a link to an article with photo's of the tool that I use to hold the crankshaft pulley:

http://forum.australia4wd.com/index.php?showtopic=7463


Aussie 1997 3.2V6 SOHC 6VD1 Holden Jackaroo SE (Isuzu Trooper/Bighorn/Monterey) 5-speed manual, rear LSD, front Lokka (manual free-wheel hubs).