Debugging Java stored procedures ....

UDB PE 8.1 on XP. Have developed a simple java stored procedure using
Development Center. Performed a "Build for Debug". Now, how do I
actually perform the debugging? There 'is' a "Debug" option available
(by right clicking the Stored procedure), but it seems to just run the
program rather than provide any help in interactive debugging (like
setting up breakpoints, observing the various values being set for
various variables etc.). Have set db2set DB2ROUTINE_DEBUG=ON but it
didn't help.

Any ideas how to perform debugging? Does an IBM Distributed Debugger
need to be installed for this? Is a trial copy of this available for
download somewhere?

TIA
Raquel.