Add field to comment form

Hi Guys, I wondered if you could suggest the best way to add another field to the comment form. What I really want is for that field’s content to be added to comment_content when it is submitted to the database.

Could the form submit go to a new php page where the info is all put into the comment field then sent on to wp-comments-post.php.

I only want the text from the additional field to go into the database under the comment_content field.

Would really appreciate any comments.

Thanks