This article will guide you to create a simple dialog / popup box which will have a webform in it.
To use this you need two modules one is Webform and other is Simple Dialog. Download and install these modules before deploying this article.
To display a webform first you need to create a webform,
We will create a simple webform to demontrate this example,
Go to "Add Content" and create a webform containing a name field and an email field.
After doing this create a simple block and add following code to it,
<a href="/my-webform" class="simple-dialog" name="webform-client-form-562" title="My Webform Title" rel="width:900;position:[center,60];">Link TItle</a>
Where href will contain url of your webform, name will have form id(To get form Id, ispect form element and you will see form id in <form> element
and <hidden> element) and title will be the text which appear on the poped up form.
Hope you have successfully implemented this on your drupal 7 project, if you are facing any problems feel free to comment.