Cannot gem isntall rails

newbie in ROR.

Win 7
ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]

run admin cmd

gem install rails --include-dependencies

then I got the error here:

ERROR: While executing gem ... (Gem::GemNotFoundException)
    Could not find rails (> 0) in any repository

follow the step to install. any idea on this error?

You need to install RubyGems first to be able to run gem install.

[]'s
Rodrigo Dellacqua