Send Mail w/PHP with time limit

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 Code:

---

<?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?

I'm not a expert in PHP but the only way I see is whenever someone send you a e-mail, the php script store the time in a txt/dat file or sql database. When the user return, you just do a quick check if your timer is done..

yeah, that's what i was thinking, but i dont know how to do the timestamp thing as well as check it against the i.p. in the text file