The answer to this question should now be in the FAQ.  Check out:

http://puma.bevd.blacksburg.va.us/macbsd/macbsd-docs/faq/

It's under section 3.

Just for a quick answer, the problem is that the installer utility does 
not have a large enough memory partition by default.  Try increasing it 
in the Get Info box.

Later.

-- 
Colin Wood                                      ender@is.rice.edu
Consultant                                        Rice University
Information Technology Services                       Houston, TX