All right, after a bit of mucking about I did get
the HelloWorld program to work on my Mac.

I saw some of the errors that you did, but
in the end it does seem to work.  Perhaps we
can try together with your laptop.

Here's my complete recipe, with all the details just in case.

0) My system is Mac OS X 10.4.4, and I'm running
   /bin/bash for my shell, as set in Terminal's preferences.
     $ 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 the "Response: -4"
error that you talked about; luckily, it isn't
needed - the "lejos" command does everything in
one go, without the two steps that lejoslink and
lejosdl do, with the intermediate HelloWorld.bin.

Type just "lejos" to get its blurb.

Anyway, that's what I got; hopefully it'll work
for you with a bit of TLC, too.  I agree that
it's finicky.  I haven't tried the motors and
sensors, but did do the HelloWorld several times;
I don't expect the other programs to be that different.