rubygems update broke ruby on OSX - ruby

Question

I was having some trouble running some Ruby scripts. While trying to get these scripts to run I tried lots of different things as well as updating rubygems as I thought this may be the problem. Since then I can't get any Ruby scripts to run.
I think that if I can revert rubygems back to it's original version I may be able to run Ruby scripts again, but I don't know how.
$ gem environment
RubyGems Environment:
- RUBYGEMS VERSION: 1.3.5
- RUBY VERSION: 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]
- INSTALLATION DIRECTORY: /Library/Ruby/Gems/1.8
- RUBY EXECUTABLE: /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
- EXECUTABLE DIRECTORY: /usr/bin
- RUBYGEMS PLATFORMS:
- ruby
- universal-darwin-10
- GEM PATHS:
- /Library/Ruby/Gems/1.8
- /Users/ryan/.gem/ruby/1.8
- /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8
- GEM CONFIGURATION:
- :update_sources => true
- :verbose => true
- :benchmark => false
- :backtrace => false
- :bulk_threshold => 1000
- REMOTE SOURCES:
- http://gems.rubyforge.org/
$ ruby -v
ruby 1.8.7 (2011-02-18 patchlevel 334) [i686-darwin10]
$ which -a ruby
/opt/local/bin/ruby
/opt/local/bin/ruby
/usr/bin/ruby
/usr/local/bin/ruby
$ which -a gem
/usr/bin/gem
/usr/local/bin/gem
Thank you for any help in advance.
Ryan
$ ruby spidr_start_at.rb
spidr_start_at.rb:1:in `require': no such file to load -- rubygems (LoadError)
from spidr_start_at.rb:1
$ cat spidr_start_at.rb
require 'rubygems'
require 'uri'
require 'spidr'
url = 'http://www.ethicalhack3r.co.uk'
puts "Spidr.start_at()"
puts
Spidr.start_at(url, :depth => 1) do |spider|
spider.every_page do |page|
puts page.url.to_s
end
end

Answer 1

It seems that you have multiple versions of ruby(and gem) installed. It is advised to use rvm when maintaining multiple ruby versions. Or clean up your wrong/old/unneeded installations.

Answer 2

For downgrading Rubygems, you can do the following:
sudo gem update --system VERSION
You obviously have to put a real version there.