Setting Up Folder Permissions For Uploading Files in IIS 6

There are so many solutions to this problem. But it all boils down to the permissions given to the account to be used in accessing a particular resource. Assuming the website is saving a document to a Windows Share on another server. You will have to give Read/Write access to your account of choice (a system account maybe that password never expires) to that particular Share. Then in the web.config file, configure impersonation to use that same account like so ...

<system.web>
     <identity impersonate="true" userName="dom1\sys-account" password="mypass"></identity />

Here's a post from msdn regarding IIS Authentication with impersonation. In particular about intranet scenarios.