I also tried to install debian behind an apt-proxy and the installations hangs when fetching packages during installation (Errormsg on ALT-F4).
It seems that all Debian etch installations behind a sarge apt-proxy fail because of apt-proxy bug 374405: > Incompatible with full URL HTTP requests from recent apt versions > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=374405 Upgrading the apt-proxy from sarge to backports.org solved the installation-problem. Bye, Wolfgang