How to compare a string to a number in and if else statement

I worked it out… this is the code I used

<?php

if(!isset($_GET['screen_check']))
{
 /* This code will be executed if screen resolution has not been detected.*/
 echo "<script language='JavaScript'>
 <!-- 
 document.location=\"$PHP_SELF?screen_check=done&Width=\"+screen.width+\"&Height=\"+screen.height;
 //-->
 </script>";
}
else 
{    
 /* This code will be executed after screen resolution is detected.*/
    if(isset($_GET['Width']) && isset($_GET['Height'])) {
 // Resolution  detected
 //echo "<h1>Your screen resolution is ".$_GET['Width']." x ".$_GET['Height'].".</h1><br />";
 //Display page as per resolution
 if(($_GET['Height']>665)) {
 //echo "<b>This will be displayed when screen resolution is greater than 1024x768.</b>";
 }
 else {
 //Display page as per resolution
 //echo "<b>This will be displayed when screen resolution is either equal to or less than 1024x768.</b>";
 }
     }
     else {
               // Resolution not detected
     }
}
?>