R help - Feb 2006 - failed installing hdf5 package--can't find zlib

I use Mac, tried to install the package hdf5-1.6. Its configuration script
can't find zlib, which 
apparently exists in my /usr directory. I used

R CMD INSTALL --configure-args=--with-hdf5=/sw 
--configure-args=--with-zlib=/usr 
hdf5....tar.gz

It still can't find zlib. Is this a bug? Any pointer is appreciated.

Zepu