how to build i386 rpms on x86_64

[Jack Howarth]

     Is there a clear procedure to be able to build i386 versions of
rpms on a Fedora Core 4 x86_64 installation? There are a few packages
like gromacs with i386 assembly optimizations which don't exist when
built as x86_64. I tried using...

linux32 rpmbuild -ba gromacs.spec

...but it seems that the required i386 parts of the gcc compiler are
not installed. In particular, I am concerned about how destabilized
my build system will become if I attempt to configure the machine to
build both architectures. Thanks in advance for any information.
           Jack