First of all, I would strongly suggest you use a more complex mail script than simply calling the mail function. Sending email by the mail() function alone has a set of security issues, one of which being that it's relatively easy for your form to be compromised and used to send spam (have had it happen to me personally).
I would suggest you use the PHP Mailer Class (http://phpmailer.codeworxtech.com/) and configure it for SMTP. Authentication of an SMTP account will make sending of mail from your server considerably more secure than just calling the mail() function directly.
Onto your IIS comment, do you use PHP elsewhere in your website? You said IIS6 without PHP support, but if you didn't have PHP support I wouldn't have expected it to actually process the PHP and give you a PHP error.
That error is telling you that the port is set incorrectly. It could be that your server does not have SMTP configured for a default port or you inputted the wrong one. Check to see what port SMTP operates on and make sure that matches your configuration.
If you don't have access to your php.ini file or simply don't want to mess with it, you can do the following at the top of your email script:
ini_set("smtp_port", "YOURPORT");
EDIT: Also, I just noticed that in your first example you haven't provided the script with the password to the email account. SMTP authentication will require the username and password for the account. If the script can't login to the mail server, it can't send your email.