By default on 10.6, gcc builds in 64-bit mode. Nav is one of the 
deprecated "classic" Macintosh platform modules and has been removed in 
Python 3.  It and many other of the deprecated Mac modules use Carbon 
interfaces that are only available in 32-bit on OS X.  If you don't plan 
to use Nav and other Carbon Mac modules, you can ignore the build errors 
about Nav (although it would be nice to make it fail a bit more 
cleanly), otherwise force the build to be 32-bit only.  Also, OS X does 
not provide a GNU readline library; if you want to use it with your 
Python, you'll need to install a local copy (for example, via MacPorts 
or building your own); otherwise you can ignore that error as while.  In 
other words, other than those missing libraries, the python you built 
should work.