Build/compile error problem in OSX (10.4.7)

Hi - new to all of this - novice would be too high a title for me... but 
I tried to install openexr 1.2.2 on my mac. I followed the instructions 
in the INSTALL file and all was well until I entered 'make install' and got:

Making install in Half
make  install-am
/bin/sh ../mkinstalldirs /usr/local/lib
 /bin/sh ../libtool --mode=install /usr/bin/install -c  libHalf.la 
/usr/local/lib/libHalf.la
/usr/bin/install -c .libs/libHalf.2.0.2.dylib 
/usr/local/lib/libHalf.2.0.2.dylib
install: /usr/local/lib/libHalf.2.0.2.dylib: Permission denied
make[3]: *** [install-libLTLIBRARIES] Error 71
make[2]: *** [install-am] Error 2
make[1]: *** [install] Error 2
make: *** [install-recursive] Error 1

Have i done something wrong / missed something...?

Thanks

Dazza