You can download a compiled package from here http://sourceforge.net/projects/cernrootdebs/
it is quite straightforward. Read the instructions.
To reply to Roland Taylor: the instructions are listed in the Readme file.
The installation requires simply a double-click on the deb archive.
"This package is going to be installed on /opt/root dir, to not conflict with Root package provided by Ubuntu repos. So you might want to create a symbolic link in /usr/bin; this is my choice:
sudo ln -s /opt/root/bin/root /usr/bin/root-latest
so you can run root from ubuntu repos typing root, or my version typing root-latest (to upgrade from a previous version packaged by me, first remove old package)"
In case root doesn't start because it doesn't find libCore.so, but these two lines in your ~/.bashrc
Enabled support for asimage, astiff, builtin_afterimage, builtin_ftgl, builtin_glew, cintex, explicitlink, fftw3, genvector, krb5, mathmore, memstat, minuit2, opengl, pgsql, python, reflex, roofit, shadowpw, shared, ssl, tmva, unuran, x11, xft, xml."