When I tried easy_install greenlet (also eventlet), as the documents said in Ubuntu 10.04 (Lucid Lynx), I got the error above.
Why is that?
And I have installed build-essential.
As I cannot take the format right here, I paste the message printed out there http://sugelawa.appspot.com/?p=35001
To use easy_install to install modules that contain C extensions (like greenlet), you need a complete development stack installed on your system. For a basic install, the means build-essential for the C part and python-all-dev for the Python part (that's where Python.h lives).
(Warning: This is Ubuntu-specific and is somewhat applicable to Debian too)