The environment property tag was added in the Ant 1.3 release.
I have the same problem.
I have downloaded ant 1.3 and untarred it and when I do 'ant -version', I get 'Ant version 1.2 compiled on October 24 2000'!
What's going on here?
(I checked to ensure the correct version was being referenced by typing 'which ant' and its running the downloaded copy called 'jakarta-ant-1.3/bin/ant')
it worked for me for ant1.3. thanks ..
aha! there were in fact two ant.jars - one I downloaded on its own and one I downloaded originally with the jboss binaries.