无法下载hpricot

在命令模式下，使用gem install hpricot，提示如下错误：请高手指点下如何处理？（执行gem update也这样了）

/********************************************************************
Building native extensions. This could take a while...
ERROR: Error installing hpricot:
   ERROR: Failed to build gem native extension.

c:/ruby/bin/ruby.exe extconf.rb install hpricot
checking for stdio.h... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.

Provided configuration options:
   --with-opt-dir
   --without-opt-dir
   --with-opt-include
   --without-opt-include=${opt-dir}/include
   --with-opt-lib
   --without-opt-lib=${opt-dir}/lib
   --with-make-prog
   --srcdir=.
   --curdir
   --ruby=c:/ruby/bin/ruby


Gem files will remain installed in c:/ruby/lib/ruby/gems/1.8/gems/hpricot-0.6.1
1 for inspection.
Results logged to c:/ruby/lib/ruby/gems/1.8/gems/hpricot-0.6.161/ext/fast_xs/ge
_make.out
/********************************************************************************