not able to update ruby (and also not able to install gems)

I am new to ruby.

OS: Windows XP 
Ruby Version --ruby 1.8.6 (2008-08-11 patchlevel 287) [i386-mswin32] 

When I run

gem update --system after installing ruby 

I am getting this error

C:\Documents and Settings\abhisheksreepal>gem update --system 
Updating RubyGems 
Updating rubygems-update 
ERROR:  While executing gem ... (Gem::InstallError) 
    invalid gem format for C:/Ruby/lib/ruby/gems/1.8/cache/rubygems-update-1.3.5.gem 开发者_运维百科

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I think it might be a corrupted download - Gems has downloaded a bad copy of the rubygems-update package into the cache, and every time that you run the update function it tries to use that cached copy.

Try deleting C:/Ruby/lib/ruby/gems/1.8/cache/rubygems-update-1.3.5.gem and trying again.

If that doesn't work, uninstall the version of Ruby that you are using now, and use the Release Candidate of RubyInstaller. The RubyInstaller supersedes the One-Click Installer, and has a newer version of RubyGems.