This post originally appeared on the Annexe.
Dependencies, gleaned from trial and error:
apt-get update
apt-get install autoconf
apt-get install libgliv2.0-dev
apt-get install libtool
apt-get install make
And building from source:
curl -O "http://wiki.qemu-project.org/download/qemu-2.1.2.tar.bz2"
cd ./qemu-2.1.2
./configure --prefix=/usr/local
make qemu-img
Should probably work in Ubuntu too, but YMMV.