Send Mail w/PHP with time limit

[BobDoleX]

i'm trying to do a form thing were people can send mail to me by filling out a forum. I also dont want people to spam me, so i want to make sure a visitor can only send mail to me every hour. How would i go about doing this? I have the following PHP coding so far..

<?php

if (isset($_POST['name']) && isset($_POST['email']))
{

    $name=$_POST['name'];
    $email=$_POST['email'];
    $caption=$_POST['caption'];

    str_replace('\"','"',str_replace("'","'",$name));
    str_replace('\"','"',str_replace("'","'",$caption));

    $to="[email protected]";
    $headers = "From: $email\n";

    $message="Name: $name\n\nEmail: $email\n\nCaption: $caption";

    if (!$name || !$email || !$caption)
    {
        echo 'You have left some areas blank.  Please fill out the form completely';
    }
    if(mail($to,"Caption",$message,"$headers"))
    {
        echo "Name: $name
Email: $email
Caption: $captionz

 Thank you, $name, for your comment. ";
    }
    else 
    {
        echo "There was a problem sending the mail. Please contact The Webmaster if this problem persists.";
    }

}

else
{
    echo "To submit a Caption, please look under \"Create a Caption\" under the navigaiton";
}
?>

I just dont know how to do the ip time limit thing, can someone help?