I am setting up my iphone project to run with hudson, my build script works fine locally, but when executing the following command on my snow leopard server mac
Schemes are per default not shared between users (and your build-server). As David mentions, you can share them, but you can also just invoke the targets instead, which are shared.
So instead of
xcodebuild -scheme Foobar
it'd be
xcodebuild -target Foobar
since schemes are normally named the same as the target.