libstdc++.so.5: cannot open shared object file - but library is installed and up-to-date

rpm hence the repo knows about shared library names and what provides them. So

yum install 'libstdc++.so.5'

wiil install whatever is necessary if the repo has it.

In your case it would fetch compat-libstdc++-33-3.2.3-66.i586.rpm and its 32-bit deps if you don't have them already because the binary you are trying to run is apparently 32-bit

libstdc++-4.4.1-2.fc11.x86_64 installs libstdc++.so.6. You need the compat-libstdc++-33-3.2.3-66.x86_64 package to get libstdc++.so.5. (Do not symlink! libstdc++.so.5 and libstdc++.so.6 are incompatible.)

yum install compat-libstdc++-33 solved this for me.