RIPEMD160 is trying to load the shared object portion of itself. This may not have been installed properly. Do you have a C compiler on your Mac? Was the RIPEMD160 XS code compiled by the C compiler? If not, you'll have to get a binary distribution of the module, made specifically for the Mac.

There's a list of MacPerl ports of CPAN modules, w/ binary distributions, at http://pudge.net/cgi-bin/mmp.plx.

If you *have* compiled the shared library, then you may just need to modify @INC. I believe this is done in the Preferences menu, under Edit, in MacPerl.