I think your problem is more one with HTML then PHP. the textarea tag does not have a value attribute like its input and other counterparts. Instead you must place the value of the text area between the opening and closing text area tags.
So you code should look something like this:
<td class = "graham"><span class = "bold">* Comment/span></td>
<td class = "graham"><textarea class="three" rows="10" name = "comment" cols="50">
<?php if(isset($_POST['comment'])) echo stripslashes($_POST['comment']);?>