Under the current system, installing gnome from RPMs is hazardous to your health. You won't get more than one GNOME app to work at a time (unless they came in the same bundle). This bug report applies to all versions of GTK rpms - even the old rpms need to be fixed (or a new rpm full of old versions created). Redhat loves to delete old versions you still need. One place this hurts you is GTK shared libraries. The shared library system is smart enough to handle multiple library versions simultaneously installed and will try to pick the closest match; Redhat screws this up by deleting the old ones. This is why you can almost never get gnome apps to work. Every gnome app typically needs a different library version (and they aren't compatible with other versions because the library calling conventions haven't stabilized, which would be fine if redhat didn't delete the old ones). Every time you install a new gnome app, you need to upgrade one or more libaries, which thanks to redhat will break all your other gnome apps.
This is not a gnome-libs issue. Installing the gtk+-1.2-xxx packages will not break existing applications which are linked against gtk+-1.0. The gtk+10 package, which is required in order to install the gtk+-1.2 package, has the required shared libraries which gtk+-1.0 apps require. The upgrade to gtk+-1.2 unless the gtk+-1.0 package exists, or you used --force to install, in which case the consequences are not guaranteed to be good.