Ruby-on-rails – Rails keeps telling me that it’s not currently installed

I use rvm to manage different rubies and their gemsets. My shell is zsh with oh-my-zsh configured with basic settings. Enabled oh-my-zsh plugins are ruby, rails, osx, and git. Here's the command I used to install ruby-1.8.7 and rails-3.0.7.

rvm install 1.8.7
rvm use 1.8.7
gem install rails -v=3.0.7

and then I typed rails and got:

Rails is not currently installed on this system. To get the latest version, simply type:

    $ sudo gem install rails

You can then rerun your "rails" command.

I've tried more thorough installs also, Like reinstall rubygems after switching to ruby-1.8.7, or create a completely new gemset, but with no luck.

Here's the rvm info:

ruby-1.8.7-p352@rails:

  system:
    uname:       "Darwin yicai.local 10.8.0 Darwin Kernel Version 10.8.0: Tue Jun  7 16:32:41 PDT 2011; root:xnu-1504.15.3~1/RELEASE_X86_64 x86_64"
    bash:        "/bin/bash => GNU bash, version 3.2.48(1)-release (x86_64-apple-darwin10.0)"
    zsh:         "/bin/zsh => zsh 4.3.9 (i386-apple-darwin10.0)"

  rvm:
    version:      "rvm 1.8.6 by Wayne E. Seguin (wayneeseguin@gmail.com) [https://rvm.beginrescueend.com/]"

  ruby:
    interpreter:  "ruby"
    version:      "1.8.7"
    date:         "2011-06-30"
    platform:     "i686-darwin10.8.0"
    patchlevel:   "2011-06-30 patchlevel 352"
    full_version: "ruby 1.8.7 (2011-06-30 patchlevel 352) [i686-darwin10.8.0]"

  homes:
    gem:          "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails"
    ruby:         "/Users/nil/.rvm/rubies/ruby-1.8.7-p352"

  binaries:
    ruby:         "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin/ruby"
    irb:          "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin/irb"
    gem:          "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin/gem"
    rake:         "/Users/nil/.rvm/bin/rake"

  environment:
    PATH:         "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails/bin:/Users/nil/.rvm/gems/ruby-1.8.7-p352@global/bin:/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin:/Users/nil/.rvm/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/local/sbin"
    GEM_HOME:     "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails"
    GEM_PATH:     "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails:/Users/nil/.rvm/gems/ruby-1.8.7-p352@global"
    MY_RUBY_HOME: "/Users/nil/.rvm/rubies/ruby-1.8.7-p352"
    IRBRC:        "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/.irbrc"
    RUBYOPT:      ""
    gemset:       "rails"

and the gem version is 1.8.10, the latest.