I'm stuck with this problem.

cat ~/.rvm/gems/ruby-1.8.7-p249/gems/nokogiri-1.4.1/ext/nokogiri/mkmf.log

Gives this errors (clipped)

conftest.c:3: error: 'xmlParseDoc' undeclared (first use in this function)
conftest.c:3: error: (Each undeclared identifier is reported only once
conftest.c:3: error: for each function it appears in.)

For several libraries which are found in the system.

If I manually go into

~/.rvm/gems/ruby-1.8.7-p249/gems/nokogiri-1.4.1/ext/nokogiri/

And compile and install everything goes fine

ruby extconf.rb
make
make install
mkdir -p /Users/tommasop/.rvm/rubies/ruby-1.8.7-p249/lib/ruby/site_ruby/1.8/i686-darwin9.8.0/nokogiri
/usr/bin/install -c -m 0755 nokogiri.bundle /Users/tommasop/.rvm/rubies/ruby-1.8.7-p249/lib/ruby/site_ruby/1.8/i686-darwin9.8.0/nokogiri

except that on script/server:

? script/server --debugger
=> Booting Mongrel
=> Rails 2.3.5 application starting on http://0.0.0.0:3000
./script/../config/../vendor/rails/railties/lib/rails/gem_dependency.rb:119:Warning: Gem::Dependency#version_requirements is deprecated and will be removed on or after August 2010.  Use #requirement
The following gems have native components that need to be built
  nokogiri  

You're running:
  ruby 1.8.7.249 at /Users/tommasop/.rvm/rubies/ruby-1.8.7-p249/bin/ruby
  rubygems 1.3.6 at /Users/tommasop/.rvm/gems/ruby-1.8.7-p249, /Users/tommasop/.rvm/gems/ruby-1.8.7-p249%global

Run `rake gems:build` to build the unbuilt gems.

Any help greatly appreciated!