I've never done this before however, if I were going to attempt it, I would only use AJAX and PHP.
I think you would have to have a 'was this helpful' link that calls an ajax function. The ajax function would go to a php page that would basically update a database each time someone clicked helpful.
If you had 2 choices (helpful or not helpful) you would have 2 columns and when displaying the result you could see which was greater of the 2 and display that as the result
Col 1 (helpful) Col 2 (Not Helpful)
Here you would use a php script to compare the 2 numbers and, as helpful is greater than not, display 'users thought this was helpful'