如何在IIS Version5.1中提供写权限？

I have developed an web application using Asp.net ( .Net Framework 3.0). In this application I have created a folder in the application directory. This folder contains an xml file to read and write data. when I tested this application in my local machine I can read and write data. But, when I deployed in IIS Ver5.1, I can read the data but when I try to write data in xMl file i could not. I have developed an web application using Asp.n