1. you can enable webforms as a block --> select the webform content
    you created, tab "Webform" > "Form Settings" > "Enable as a block"
    
 2.   put the block inside a region, I've put mine in the footer region
 
 3.  CSS style the footer webform block as "display: none;"
    
 4.  for colorbox: in "configuration", "Media", "Colorbox" --> advanced
    settings, activate "Enable Colorbox inline"
    
 5.   add this as the html code for opening the colorbox webform link: 
   

>`<a class="colorbox-inline" href="?width=310&amp;height=460&amp;inline=true#name-of-your-block">`

You can also display the webform in popup using [Colorbox Node][1] module.

> Gives the user the ability to display ANY page inside a colorbox modal
> without the header and footer. Those pages include:
>
   - Node Pages
   - User Pages
   - Views Pages
   - **Webforms (requires Webform Ajax Module)**
   - Integration with Views
   - Integration with Context
   - Integration with Panels








  [1]: https://drupal.org/project/colorbox_node