At the moment minecraft dev is only for the 1.6 snapshots which due to requiring java 6 will not run on 10.5.8 or earlier because these versions of OSX only support up to Java 5.
Saren Currie
At the moment minecraft dev is only for the 1.6 snapshots which due to requiring java 6 will not run on 10.5.8 or earlier because these versions of OSX only support up to Java 5.