Please checkout the branch according to the version of Drupal you're running...

Drupal 4:
  DRUPAL-4-7

Drupal 5:
  DRUPAL-5--3

Drupal 6:
  DRUPAL-6--1

HEAD contains an experimental branch for Drupal 6

COMPATIBILITY WITH OTHER MODULES:
CCK EMAIL FIELD: When using the field display option 
"email contact form" the form_id for CAPTCHA(->admin/user/captcha) should be "email_mail_page_form".