I am new to ruby. I have installed Ruby on Rails on my XP but its failing on the last step of updating rails.

When I type: gem update

I get the following message:

Updating installed gems
Updating hpricot
Building native extensions. This could take a while...
ERROR: While executing gem ... (Gem::Installer::ExtensionBuildError)
ERROR: Failed to build gem native extension.

C:/InstantRails-2.0-win/ruby/bin/ruby.exe extconf.rb update
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:

Gem files will remain installed in C:/InstantRails-2.0-win/ruby/lib/ruby/gems/1.
8/gems/hpricot-0.6.161 for inspection.
Results logged to C:/InstantRails-2.0-win/ruby/lib/ruby/gems/1.8/gems/hpricot-0.


anyone pls help