The installer ran cleanly, but any attempt to execute regina or rexx results in a "Bus error" and no processing occurs (whether it's just "regina" and assumed a wait for interactive input, or providing a simple file ... the result is the same).
What do you see for these commands:
$ which rexx
$ which regina
$ rexx -v
REXX-Regina_3.4 5.00 30 Dec 2007
I am on 10.5.3, though.