I have a debian etch box im wanting to backup. I have another box I can put a new hard drive into...however I already have Sidux which is a branch distro of debian sid. Can ISPConfig run on Debian Sid alright?
Debian Sid is unstable and always be unstable. There is no reason to run Debian Sid unless you are a developer or similar. See http://www.debian.org/releases/unstable/