OK, here's a working version (well it worked for me anyway)
<?
header ("Content-type: application/pdf");
$file = fopen ("/path/to/file.pdf", "r");
$contents = fread ($file, filesize("/path/to/file.pdf"));
echo $contents;
fclose ($file)
?>
just tested in ie 6.0 & opera 5.12, works great in both. (NT versions)