setting up jikes on Linux with Blackdown

I've recently set up an older Mac running Linux (YDL 3.0.1) at home that I want to use for some Java development. I've installed IBM's Blackdown (1.4.2 SDK) rpm. I installed jikes (1.22) because, though javac works fine, any speed benefit I can get on this will be helpful, and I hear jikes beats javac in performance. My problem is that jikes wants the classpath set, but I don't know what to set it to. (I wish I knew what javac was using.) Normally I'd make sure to set it so that rt.jar is included for starters, but I can't find the jar! Anybody with jikes/Blackdown experience out there have any pointers for me? Sure would appreciate it.