(This advice is for those using x86_64 Linux)
you may also need to do:
apt-get install multiarch-support ia32-libs
Of course apt-get is only for Debian and Debian-derived systems, ie Ubuntu, Mint, etc.
For 64-bit Red Hat Enterprise Linux (RHEL), CentOS, and Fedora. etc:
yum install compat-libstdc++-33.i586 gtk+.i586 gtk2.i586
or for later version of the system:
yum install compat-libstdc++-33.i686 gtk+.i686 gtk2.i686
64-bit installation of OpenSUSE 11
yast -i gtk2-32bit
This is what I'm told, although I have not tested those others.