So I noticed steam had got released today (A bit late I know)
But I tried it out on Backtrack 5 and it threw a few errors at me.
So here's how to get it running on Backtrack 5.

This method worked fine for me, No problems with Backtrack at ALL. But I do advise you to use this at your own risk.

Download & Install the Steam.deb

gedit /usr/bin/steam

Comment out like so.

# Don't allow running as root
#if [ "$(id -u)" == "0" ]; then
# show_message --error $"Cannot run as root user"
# exit 1
#fi

nano /etc/apt/sources.list


Add the ubuntu 12.04 repo.

#ubuntu 12.04
deb http://us.archive.ubuntu.com/ubuntu/ quantal main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ quantal main restricted

Update APT:
apt-get update

Install libc6
apt-get install libc6

Then comment out Ubuntu repos

Update APT:
apt-get update

Install the following:
apt-get install libgl1-mesa-dri jockey-common libgl1-mesa-glx

Then you're good to go enjoy steam on Backtrack, Hack all the things, Play all the games.

Emery.