You must install the Snow Leopard version of the iPhone SDK ( iphone_sdk_3.0_gm_seed__snow_leopard.dmg ), not a copy of Leopard ( iphone_sdk_3.0_gm_seed__leopard__9m2736.dmg ). My suggestion was to run the following and then install a copy of the Snow Leopard SDK again:
sudo /Developer/Library/uninstall-devtools
source share