How to intall ruby local?

when i use
gem install rails
there error happened as below:
Attempting local installation of ‘rails’
Local gem file not found: rails*.gem
Attempting remote installation of ‘rails’
ERROR: While executing gem … (Errno::EBADF)
Bad file descriptor -connect(2)

i used ruby184-16_rc1 in windows_xp_sp2.
and i download the zip package,but i don’t know how to install it.
pls help me. thanks.