Installing Mobi2Mobi on a Mac can be a pretty annoying process. If your error messages have to do with "XXX not found", what you do is head over to Perl's CPAN site, type in the name of the missing module it's complaining about, and install that before trying again with the particular piece you're trying to install.
You'll probably have to do it a number of times. Some of the dependencies go down to about 5 levels deep, if I recall correctly. But once you've got the stuff in place, you never have to touch it again.
Except if you also have MacPorts or similar and it's trumped the built-in/your usr/local added Perl install, in which case you'll have to reset the PATH or you'll get an error message when using Mobi2Mobi.
They've also got
EBook-Tools over at CPAN, which is an alternative which gives you 1-step unpacking/conversion to/from other formats. You'll need to tie it into KindleGen for Mobi generation, though.