iis - PHP mkdir() and move_uploaded_file() Permission Denied with 777

I am writing a PHP script for a client which will be installed on a server which I do not have back-end access to. I only have access to a particular folder and database.

My script will upload files and create folders. However I get a permission denied error when I try run mkdir() and move_uploaded_file(). Here are the conditions:

Server running IIS 6 and PHP 5.1.2 (a bad, ancient mixture, I know)
Folder where I try to make a directory and upload a file has 777 permissions
Folder all the way up to the web root has 777 permissions
File uploads are on
Uploaded file is very small, within the upload_max_filesize range
Any ideas on why this isn't working?

Thank you for your time.