Start by installing rvm. Dealing with ruby on a linux system without it is a nightmare.
$ bash < <(curl -s https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer)
Install zlib
rvm pkg install zlib
You may also need to install zlib.
aptitude install zlib1g-dev
or
apt-get install zlib1g zlib1g-dev zlibc
Upgrade to the latest version of Ruby.
rvm install 1.9.2 --with-zlib-dir=$rvm_path/usr --with-openssl-dir=$rvm_path/usr
Not doing the above resulted in:
ERROR: Loading command: update (LoadError)
no such file to load -- zlib
ERROR: While executing gem ... (NameError)
uninitialized constant Gem::Commands::UpdateCommand
Set Ruby 1.9.2 to be the default version
rvm --default use 1.9.2
Update the System so it has knowledge of all the gems etc.
rvm gem update --system
Install Selenium Web Driver