Check whether a directory exists in PHP

I know, I know, this sounds soo easy. But I can't seem to find the correct answer on the Internet.

One of the solution I found was to use is_dir.

if(is_dir($dir))
  echo 'directory exists';
else
  echo 'drectory not exist';

But this is wrong-- All this function does is to check whether the $dir is a directory, it doesn't check whether the directory exists, or not. In other words if I put:

$rootDir = "C:\\Documents and Settings\\test\\My Documents\\Image Directory\\Me Dog\\";

then the function will return a true, even though you can find no such directory on your web server.

Any ideas?