具體過程如下：
1、InstantRails-2.0安裝后，在配置環境變量path中配置ruby/bin目錄（如果系統中有多個RUBY，執行命令行的時候系統認的就是path中的）
2、進入DOS命令行，執行gem update --system，結果
Updating RubyGems...
ERROR: While executing gem ... (Gem::RemoteSourceException)
HTTP Response 302 fetching http://rubygems.org/yaml
這是因為gem的配置過低，無法進行遠程更新，執行gem -v 發現是1.0.1
3、從下面這個地址下載 rubygems-update-1.3.7.gem，http://rubyforge.org/frs/download.php/70695/rubygems-update-1.3.7.gem
然后DOS命令進行該文件所在的目錄，執行gem install --local rubygems-update-1.3.7.gem，出現信息
Successfully installed rubygems-update-1.3.7
1 gem installed
Installing ri documentation for rubygems-update-1.3.7...
Installing RDoc documentation for rubygems-update-1.3.7...
Could not find main page README
Could not find main page README
Could not find main page README
Could not find main page README
執行gem -v查看，發現并沒有更新成功，Could not find main page README是什么意思我沒弄明白，但是我從http://production.s3.rubygems.org/yaml上發現這么一句
If you have an older version of RubyGems installed, then you can still
do it in two steps:
$ gem install rubygems-update # again, might need to be admin/root
$ update_rubygems # ... here too
我照著再執行 update_rubygems，接著出現的信息很多，就不帖出來，再執行gem -v，發現更新成功，已經是1.3.7了
這一步是一切成功的源泉！！！！！！
4、接著再執行gem update --system，提示
Updating RubyGems
Nothing to update
這是為什么我不明白，請高手指點一下
5、再執行gem update rails --include-dependencies，提示信息
Updating installed gems
Updating rails
ERROR: Error installing rails:
actionpack requires rack (~> 1.0.0, runtime)
Gems updated: activesupport, activerecord
Installing ri documentation for activesupport-2.3.3...
Installing ri documentation for activerecord-2.3.3...
Installing RDoc documentation for activesupport-2.3.3...
Installing RDoc documentation for activerecord-2.3.3...
執行rails -v，發現還是2.0.2沒有更新成功，根據actionpack requires rack (~> 1.0.0, runtime)，應該是actionpack 需要1.0.0版本的rack
6、執行gem install rack -v=1.0.0
Successfully installed rack-1.0.0
1 gem installed
Installing ri documentation for rack-1.0.0...
Installing RDoc documentation for rack-1.0.0...
更新成功
7、再次執行 gem update rails --include-dependencies
出現信息
Updating installed gems
Updating rails
Successfully installed rake-0.8.7
Successfully installed activesupport-2.3.8
Successfully installed activerecord-2.3.8
Successfully installed rack-1.1.0
Successfully installed actionpack-2.3.8
Successfully installed actionmailer-2.3.8
Successfully installed activeresource-2.3.8
Successfully installed rails-2.3.8
Gems updated: rake, activesupport, activerecord, rack, actionpack, actionmailer, activeresource, rails
Installing ri documentation for rake-0.8.7...
Installing ri documentation for activesupport-2.3.8...
Installing ri documentation for activerecord-2.3.8...
Installing ri documentation for rack-1.1.0...
Installing ri documentation for actionpack-2.3.8...
Installing ri documentation for actionmailer-2.3.8...
Installing ri documentation for activeresource-2.3.8...
Installing ri documentation for rails-2.3.8...
Installing RDoc documentation for rake-0.8.7...
Installing RDoc documentation for activesupport-2.3.8...
Installing RDoc documentation for activerecord-2.3.8...
Installing RDoc documentation for rack-1.1.0...
Installing RDoc documentation for actionpack-2.3.8...
Installing RDoc documentation for actionmailer-2.3.8...
Installing RDoc documentation for activeresource-2.3.8...
Installing RDoc documentation for rails-2.3.8...
執行rails -v，發現已更新成功
總結：rails更新有兩種方式：1、聯機更新;2本地更新
聯機更新過程中如果出現HTTP Response 302 fetching http://rubygems.org/yaml無法更新，有兩種情況
一是gem的版本過低，二是與服務器的連接不通
此時可以試著加入其他服務器地址
gem source -l 查看列表
gem source -a http://rubygems.org 加入新的服務器地址
或者直接gem install rubygems-update --source http://rubygems.org
本地更新需要下載相應的gem包，版本需與要更新的rails版本對應，同時安裝順序有要求，因此gem包之間有依賴關系
順序從上面的顯示信息中可以看出來
Successfully installed rake-0.8.7
Successfully installed activesupport-2.3.8
Successfully installed activerecord-2.3.8
Successfully installed rack-1.1.0
Successfully installed actionpack-2.3.8
Successfully installed actionmailer-2.3.8
Successfully installed activeresource-2.3.8
Successfully installed rails-2.3.8
至于gem包的下載地址都在http://rubyforge.org/，但是有些項目的并不好找到，可以在google中直接搜索，就能找到在http://rubyforge.org/中的地址。
一天，一個月，一年。總有一天會變得不一樣。