require 'z' not working

[Brian Takita]

Hello,

I'm trying to install libxml. I ran extconf.rb and got the result:

checking for socket() in socket.lib... no
checking for gethostbyname() in nsl.lib... no
checking for atan() in m.lib... yes
checking for inflate() in z.lib... no
extconf failure: need zlib

I tried doing the require 'z' command in irb and got the error:
LoadError: No such file to load -- z
from c:/Program
Files/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:18:in
`require__'
from c:/Program
Files/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:18:in
`require'
from (irb):6

However, require 'zlib' works.
Is there a way to get require 'z' to work?

I'm using Ruby 1.8-15 with the Windows one click installer package. My
OS is Windows XP.

Thank you,
Brian Takita