Redmine

at first i am a newbie!

So i try to install redmine-2.0.2 on my local mac. But he can't install json (1.7.3).

Fetching gem metadata from http://rubygems.org/.......
Using rake (0.9.2.2) 
Using i18n (0.6.0) 
Using multi_json (1.3.6) 
Using activesupport (3.2.5) 
Using builder (3.0.0) 
Using activemodel (3.2.5) 
Using erubis (2.7.0) 
Using journey (1.0.3) 
Using rack (1.4.1) 
Using rack-cache (1.2) 
Using rack-test (0.6.1) 
Using hike (1.2.1) 
Using tilt (1.3.3) 
Using sprockets (2.1.3) 
Using actionpack (3.2.5) 
Using mime-types (1.18) 
Using polyglot (0.3.3) 
Using treetop (1.4.10) 
Using mail (2.4.4) 
Using actionmailer (3.2.5) 
Using arel (3.0.2) 
Using tzinfo (0.3.33) 
Using activerecord (3.2.5) 
Using activeresource (3.2.5) 
Using bundler (1.1.4) 
Using coderay (1.0.6) 
Using fastercsv (1.5.5) 
Installing json (1.7.3) with native extensions 
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb 
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/ruby.h

Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/json-1.7.3 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/json-1.7.3/ext/json/ext/parser/gem_make.out
An error occured while installing json (1.7.3), and Bundler cannot continue.
Make sure that `gem install json -v '1.7.3'` succeeds before bundling.

What's my Problem? I don't know what to do.

If u need more informations say it.

Thanks...

edit:

*** LOCAL GEMS ***

actionmailer (3.2.5)
actionpack (3.2.5)
activemodel (3.2.5)
activerecord (3.2.5)
activeresource (3.2.5)
activesupport (3.2.5)
arel (3.0.2)
builder (3.0.0)
bundler (1.1.4)
coderay (1.0.6)
diff-lcs (1.1.3)
erubis (2.7.0)
fastercsv (1.5.5)
hike (1.2.1)
i18n (0.6.0)
journey (1.0.3)
mail (2.4.4)
mime-types (1.18)
multi_json (1.3.6)
permutation (0.1.8)
polyglot (0.3.3)
rack (1.4.1)
rack-cache (1.2)
rack-ssl (1.3.2)
rack-test (0.6.1)
rake (0.9.2.2)
rdoc (3.12)
sdoc (0.3.16)
sprockets (2.1.3)
thor (0.15.2)
tilt (1.3.3)
treetop (1.4.10)
tzinfo (0.3.33)