具体过程如下：
1、InstantRails-2.0安装后，在配置环境变量path中配置ruby/bin目录（如果系统中有多个RUBY，执行命令行的时候系统认的就是path中的）
2、进入DOS命令行，执行gem update --system，结果
Updating RubyGems...
ERROR: While executing gem ... (Gem::RemoteSourceException)
HTTP Response 302 fetching http://rubygems.org/yaml
这是因为gem的配置过低，无法进行远程更新，执行gem -v 发现是1.0.1
3、从下面这个地址下载 rubygems-update-1.3.7.gem，http://rubyforge.org/frs/download.php/70695/rubygems-update-1.3.7.gem
然后DOS命令进行该文件所在的目录，执行gem install --local rubygems-update-1.3.7.gem，出现信息
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
执行gem -v查看，发现并没有更新成功，Could not find main page README是什么意思我没弄明白，但是我从http://production.s3.rubygems.org/yaml上发现这么一句
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
我照着再执行 update_rubygems，接着出现的信息很多，就不帖出来，再执行gem -v，发现更新成功，已经是1.3.7了
这一步是一切成功的源泉！！！！！！
4、接着再执行gem update --system，提示
Updating RubyGems
Nothing to update
这是为什么我不明白，请高手指点一下
5、再执行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...
执行rails -v，发现还是2.0.2没有更新成功，根据actionpack requires rack (~> 1.0.0, runtime)，应该是actionpack 需要1.0.0版本的rack
6、执行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、再次执行 gem update rails --include-dependencies
出现信息
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...
执行rails -v，发现已更新成功
总结：rails更新有两种方式：1、联机更新;2本地更新
联机更新过程中如果出现HTTP Response 302 fetching http://rubygems.org/yaml无法更新，有两种情况
一是gem的版本过低，二是与服务器的连接不通
此时可以试着加入其他服务器地址
gem source -l 查看列表
gem source -a http://rubygems.org 加入新的服务器地址
或者直接gem install rubygems-update --source http://rubygems.org
本地更新需要下载相应的gem包，版本需与要更新的rails版本对应，同时安装顺序有要求，因此gem包之间有依赖关系
顺序从上面的显示信息中可以看出来
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包的下载地址都在http://rubyforge.org/，但是有些项目的并不好找到，可以在google中直接搜索，就能找到在http://rubyforge.org/中的地址。