HTTP 404 - File not found
First of all be sure that the default document list contains the page you are requesting (IIS -> Server Node -> Site node -> right mose click -> Properties -> Documents
Also set the necessary permission to the web folder (NETWORK SERVICE must have read/write rights)
Check if the asp.net status is allowed (IIS -> Server Node -> Web Service Extensions -> Asp.net must be allowed). This can be done during the installation of IIS.