Making a PHP Script "Very" Cache Friendly

Searching through the archives, most people are running away from caching php scripts. Im trying to do the opposite. I have a script that fetches css files. Im trying to add header() calls to it so that browsers can cache it like a normal css file. This is what I have at the top of the file -> ---------- header('Content-type: text/css'); header('Expires: ' . gmdate('D, d M Y H:i:s', time() + 3600) . ' GMT'); header('Last-Modified: ' . gmdate('D, d M Y H:i:s', filemtime('./foo.php')) . ' GMT'); -------- For the life of me, according to the output of ethereal (a network sniffer), this file is always fetched from the server. Yes I did breeze by the HTTP 1.1 spec, but I didn't pick up on anything special that I should be doing. Is there a way to make the file be put into cache, or am I barking up the wrong tree. Thanks for your insight.