This is really good to know. In Windows Server 2008 R2, not pre R2 and not Windows 7, you can add the app pool account to directories that need web permissions. You do this by directly typing in the name of the account which follows the naming standard IIS APPPOOL\
The is the name as it appears in IIS Manager. Expand the name of the web server > Sites > Name of the website appears here. If you do not see the name of the website then you have not set it up. If you are using a remote hosting provider for ASP.NET then it will depend on the name that you created the website as.
Reference article...from serverfault.com