Check the permission settings for your directory, first. You may find that the default installation of your server is preventing you from writing to a folder. If that's the case, you may need to set up a new, virtual directory.
I develop on a Win 2000 server and host on UNIX. To solve the path problems, I use this statement:
$siteHost = getenv('HTTP_HOST');
switch ($siteHost):
case "localhost":
$file_path = "C://Inetpub/wwwroot";
break;
/ Use environment to get remote hosted Apache doc roots /
default:
$file_path = $_SERVER['DOCUMENT_ROOT'];
endswitch;
Hope this helps.