Contact form 7 can be used for different kinds of forms. Sometimes we may need to show the form in popup display. For to show the contact form in popup we can simply install Easy fancybox and Contact Form 7 from wordpress plugin directoy and simple configure as below,
Firstly create contact form as you required and place contact form shortcode as below
<a href="#contact_form_pop" class="fancybox">Contact Us</a>
<div style="display:none" class="fancybox-hidden">
<div id="contact_form_pop">
Error: Contact form not found.
</div>
</div>
For further detail you may visit to url below,
Source : http://geektastical.com/2011/05/how-to-create-a-pop-up-wordpress-email-contact-form/