Comment Form Input URL

Hi community,

I hope my request will be a rather small problem.
I would like to modify the comment form.
The commenter-names are linked to a mailto-function by default.
I would like to replace this function with a http-reference so the commenter can leave his website URL instead of the e-mail address.

First of all I got the change the

<tr>
   <td>Name:</td>
   <td><input type="text" name="name" size="30"> *required</td>
</tr>
<tr>
   <td>E-Mail:</td>
   <td><input type="text" name="mail" size="30"></td>
</tr>

And I guess a gotta change the php-function somewhere.
Would you please help me modify?

Thanks in advance