I was unable to (load "fi-site-init") successfully until I commented
out the indicated line in fi-site-init.el :

(when (eq fi::emacs-type 'xemacs19)
    (load "fi-leep0.elc"))
;;    (load "fi-leep-xemacs.el"))

Until I commented this out, I got an error message about 
"too many arguments" (though I'm not sure which function xemacs
was talking about).

Perhaps 19.15 has fixed some things that made fi-leep-xemacs necessary,
and so we don't need to load it anymore ? In any case, this might 
help someone who is trying to run ACL with xemacs 19.15. (19.15 is
the latest version available at www.xemacs.org.)

Eugene Koontz