Working with Identity Impersonate from code behind

I have an application where I'm storing files into a network Folder. I have set the permission of the folder to write for "Everyone". Still its showing me "Unauthorized access". So, I thought of going withIdentity. I cannot write my username and password in the web.config since it will be readable. So, I'm trying to override the data with Username and password from code behind. But when i run the application it doesnt work and says "Unauthorized access". Here are the steps which I have followed.
In web.config i have set
<identity impersonate="false" /> Now from coding I'm changing identity properties like this.
System.Configuration.Configuration configuration = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("/"); System.Web.Configuration.IdentitySection id = (System.Web.Configuration.IdentitySection)configuration.GetSecti ...