The request to support -XX:+HeapDumpOnCtrlBreak on 1.4.2 and 5.0 update release is tracked by:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6454676
We're currently working on a fix for it and will determine which update release it will go into.
BTW, -XX:+HeapDumpOnCtrlBreak is currently an unsupported option in JDK 1.4.2 but will become supported when 6454676 is fixed.