On the very latest release of OS X Panther (7B21), Ruby 1.8 Preview 5
compiles (w/gcc 3.3) without any problems…including openssl, syck,
etc.
It still does not build readline support because of OS X’s
configuration…not Ruby’s. Its still possible to build with a bit of
work. I will try and contact Apple with hopes to have readline in the
Ruby that is distributed with Panther this fall…it really helps the
IRB experience 
Thanks to the team!
-rich