Where are X includes

[franck.legall@wanadoo.fr]

I am trying to compile messenger. When I do ./configure I have got :


franck@albert[/tmp/messenger-0.0.3] $ autoconf
franck@albert[/tmp/messenger-0.0.3] $ ./configure
loading cache ./config.cache
checking how to run the C++ preprocessor... g++ -E
checking for X... configure: error: Can't find X includes. Please check
 your installation and add the correct paths!     

Where should be thois include files ? I didn't ound them. Should I install any specific
package ?

Thanks
Franck