ERROR: While executing gem ... (Gem::GemNotFoundException) Could not find rubygems-upodate (> 0) in the repository

I got this error in my pc.At first i have installed rails 2.0.2.When i installed other package my rails 2.0.2 has been removed and i got the error like this.
ERROR: While executing gem ... (Gem::GemNotFoundException)
Could not find rubygems-upodate (> 0) in the repository

then i searched in the net and got some steps to solve.I didnt test this diff os.i have tested only in my ubuntu linux 7.10
1.gem install rubygems-update
2.sudo gem update --system
3. gem install rails -y i has thrown one error /usr/bin/gem:23: uninitialized constant Gem::GemRunner (NameError)


4.vim /usr/bin/gem
5.added require 'rubygems/gem_runner' after require 'rubygems' for more details u can view from
here
6.gem install rails -y
I has show like this
INFO: `gem install -y` is now default and will be removed
INFO: use --ignore-dependencies to install only the gems you list
Bulk updating Gem source index for: http://gems.rubyforge.org/
Bulk updating Gem source index for: http://gems.rubyforge.org/
Successfully installed rake-0.8.1
Successfully installed activesupport-2.0.2
Successfully installed activerecord-2.0.2
Successfully installed actionpack-2.0.2
Successfully installed actionmailer-2.0.2
Successfully installed activeresource-2.0.2
Successfully installed rails-2.0.2
7 gems installed
Installing ri documentation for rake-0.8.1...
Installing ri documentation for activesupport-2.0.2...
Installing ri documentation for activerecord-2.0.2...
Installing ri documentation for actionpack-2.0.2...
Installing ri documentation for actionmailer-2.0.2...
Installing ri documentation for activeresource-2.0.2...
Installing RDoc documentation for rake-0.8.1...
Installing RDoc documentation for activesupport-2.0.2...
Installing RDoc documentation for activerecord-2.0.2...
Installing RDoc documentation for actionpack-2.0.2...
Installing RDoc documentation for actionmailer-2.0.2...
Installing RDoc documentation for activeresource-2.0.2...