Error trying to install rubygems on Ubuntu

I downloaded and unpacked rubygems-1.3.4 and when I try to execute
setup I get the following message.

sudo ruby setup.rb
./lib/rubygems.rb:11:in require': no such file to load -- etc (LoadError) from ./lib/rubygems.rb:11 from setup.rb:24:inrequire’
from setup.rb:24

can anyone help me resolve this?