the ming32 gtk package seems to be build without input methods. For instance the file /etc/gtk-2.0/gtk.immodules is not present in the package, while it is included in the upstream gtk win32 binaries.
The file gtk.immodules has been added in mingw32-gtk2-2.17.11-3.fc12 : http://koji.fedoraproject.org/koji/buildinfo?buildID=132819