I keep getting invalid gem when i try to install rails??

$sudo gem install rails -v=2.1.2

With ActivRecord, ActiveSupport they all give problems when I download the gems with lynx and install them with:

$sudo gem install --local activerecord-2.1.2.gem

It does install but it kinda sucks does anybody know a solution. I just wanna try out redmine, but it seems rails app tend to break easy even with a minor update in framework