Hi Rikard!
This seems to be a problem with the upgrade to Leopard. See
http://lists.apple.com/archives/java-dev/2007/Nov/msg00371.html.
I'm afraid we don't have a solution for this, since you already tried to set -Djava.awt.headless=true. JBossIDE has the same problem (
http://jira.jboss.org/jira/browse/JBIDE-1376) and they are waiting for Eclipse 3.3.2 to fix it.
Regards,
Lars