Creating an Easy Print Button on Drupal Webforms
Basically you just add in the following code:
<div id="edit-actions" class="form-actions form-wrapper"><input id="edit-submit" class="form-submit" value="Print" name="print" onclick="window.print()" type="button" /></div>
This was tested on a D6 site, but the same idea should work perfectly on D7 sites. Enjoy!