> The current httrack debian package asks for
>   libc6 >= 2.2.5-13
> The current stable tree contains
>   libc6 2.2.5-11.2
> Any way to stick with the stable libc6 or do I need
> to install an unstable libc6?
The current debian.httrack.com binaries are a bit 
experimental, and the best way is to recompile the original 
package.

First add these sources to your /etc/apt/sources.list:
deb <http://debian.httrack.com> unstable main
deb-src <http://debian.httrack.com> unstable main

Than, use:

cd /tmp
apt-get update
apt-get source -b httrack
dpkg -i httrack*.deb