Don,
To run the PSP in GUI mode, you'll need to ensure the following libraries are in the /usr/X11R6/lib directory:
libXi.so
libXext.so
libX11.so
You can install a single RPM that will contain all the 32-bit library requirements that the PSP needs for GUI mode. The file you need to install is "xorg-x11-libs-6.7.1-23.EL.i386.rpm".
You are correct in your assumption that these need to be in the 32-bit directory, through I think you can use the x86_64 versions of the files as they are just linked to.
If you don't want to go through the hassle, you can also install the PSP in console mode by using the /nui switch. This will bypass the requirement on those libraries. If you want the capability to select which components to install in console mode, you can also include the /y switch (ie ./install780.sh /nui /y) and you will be prompted for each component.
Let me know if you have additional issues.
Regards,
Michael Garner
HP Linux PSP Developer