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:in `require'   from setup.rb:24

can anyone help me resolve this?