Just want to make sure..
First are you using the right rxvt with the GB encoded complied with it....
if not.. some time when you load the font into the term.. it will crash.
(if you are using Debian package it should call grxvt)
Second did you check the GB Xlocale is locate in your
/usr/X11R6/lib/X11/locale/zh_GB/XLC_LOCALE
directory if not you may need to download that.. if that's not your problem
I don't know ... sorry I don't use chinput
Good luck
Alex