Here's the recipe I used to get the LeJOS system up and running
as of Feb 2006.

0) My system is Mac OS X 10.4.4 running on a Powerbook G4 15" laptop.
   The following shell scripts are running in the /bin/bash shell.
   Java and gcc are both with my PATH, and show versions
     $ java -version
      ...  1.4.2_09
     $ gcc --version
      ... powerpc-apple-darwin8-gcc-4.0.0 20041026

1) downloaded lejos_2_1_0.tar.gz to /Users/mahoney/src
2) unpack and set up
     $ cd ~/src
     $ tar zxf lejos_2_1_0.tar.gz
     $ cd lejos_2_1_0
     $ mkdir jims_stuff            a place to put the rest
     $ cd jims_stuff

3) patch vmsrc/threads.c to read
      done_pi:
               ;
      #endif //PI_AVOIDANCE

4) create jims_stuff/lejos.env containing
     export LEJOS_HOME=/Users/mahoney/src/lejos_2_1_0
     export PATH=$PATH:$LEJOS_HOME/bin
     export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH:$LEJOS_HOME/bin
     export CLASSPATH=$CLASSPATH:$LEJOS_HOME/lib:.
     export RCXTTY=usb

5) from jims_stuff
     $ . lejos_env
     $ cd ..
     $ make                        lots of warnings, but finishes
     $ cd jims_stuff

6) plugged in a USB tower to the left USB port on my Powerbook G4
   (there's also a USB port on the right side; haven't tried it),
   plugged in a brick to its power adapter, turned it on,
   and put em about an inch apart, out of direct sunlight
   (saw some problems with light polution a few years back)

7) download the firmware
     $ lejosfirmdl
        (green light goes on in tower; brick beeps)
     ... 100%

8) finally transfer a program while the brick is still
   in a receptive state (after lejosfirmdl or power cycle)
     $ cp ../examples/hworld/HelloWorld.java .
     $ lejosc HelloWorld.java
        (creates HelloWorld.class)
     $ lejos HelloWorld
        (green light goes on, brick counts...)
     $  (success!)

9) hit the "run" button on the brick and see "hELL o  worL d".

The "lejosdl" command gave me a "Response: -4" error; luckily, I don't need it.

The discussion form 
  http://lists.sourceforge.net/lists/listinfo/lejos-discussion
talks about various difficulties with IR tower to brick connection;
in particular, that they must be close together and in a low light
environment.