Ah, I starting everything afresh (after individually compiling the lisp files as you suggested), and it works now.
CL-USER> (format t "~A ~A ~A ~A" (machine-type) (machine-version) (lisp-implementation-type) (lisp-implementation-version))
Power Macintosh PowerBook5,4 OpenMCL Version 1.1-pre-070722 (DarwinPPC32)
Thanks for your help. Hopefully I'll get a chance to investigate why it doesn't work 'out of the box' at some point.
T