How to get IA-32 compatibility with X86-64

[Yasha Karant]

We are using a 64 bit installation into 3D visualisation workstations, 
but need full IA-32 library compatibility.  My understanding is that 
there is no polymorphism between 32 bit and 64 bit applications by 
default, but there is for libraries:
/usr/lib versus /usr/lib64 and the like.  However, when I attempt to set 
both the x86-64 and the ia-32 repos via the "Add/Remove Software" GUI 
(e.g., Scientific Linux 6x - i386 fpr the ia-32 portion), I only get a 
list of the RPMs for x86-64 (both the platform and the SL environment) 
but not ia-32.  How does one activate both to appear so that the library 
packages for both will be put into the system via the GUI?

I have done this successfully in the past, but have seem to have 
misplaced the syntactic instructions for how to do this.

Yasha Karant