Problem resolved -- I had another library which is incompatible with libstdc++.so.5 ... and everything was fine again after I removed it.
(First of all, I'm new here and I apologize if I'm posting my question in a wrong place.) I'm having a very annoying problem: I did a clean install of Fedora 8, which comes with KDE 3.5.8. It appears that it's linked to libstdc++.so.6. Everything worked fine until I installed a the rpm that provides libstdc++.so.5 (compat-libstdc++-33). I did it because some of my other applications, like the intel compiler icc/ifort/idb depend on libstdc++.so.5. Then most KDE applications stopped working, e.g. ...