Does the system you are trying to install onto have network access?
If not then you'll need to download the roo gem to another system and
somehow get a copy of the gem onto this system.
Also be sure that you are up to date with the rubygems installer
gem update --system
Joe
P.S. It appears that you are running a very, very, very old version of
Watir.
Strongly suggest that you upgrade to at least Watir v1.9.2.
gem install watir -v1.9.2