I am using a php form processor and would like to stop web addresses from being input into the text fields.

A couple examples of what I have in place and general syntax:

PHP Code:
if (strlen($_POST['comments']) > 255 )
{
header("Location: http://www.websitename.com/error.php");
exit;
}
if (! ereg('[A-Za-z0-9_-]+\@[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+', $_POST['vis_email']))
{
header("Location: http://www.websitename.com/error.php");
exit;
} 
I've tried a couple of different things (which I haven't added above) but can't seem to get the right combination of single quotes, quotes, or brackets.
Any help would be GREATLY appreciated!!!!!!!!!!