add this to /etc/apt/sources.list (replace the mirror with one next to you if you want):
deb ftp://ftp.de.debian.org/debian/ unstable main non-free contrib
deb-src ftp://ftp.de.debian.org/debian/ unstable main non-free cont
add this to /etc/apt/apt.conf.d/01local (the name of the file does not matter, as long as it's in the same directory):
APT::Default-Release "testing";
then run
apt-get update
apt-get -t unstable install ia32-libs-gtk
there may be things which can break your system, though. remember, it's unstable.