I have recently move my Web application from Windows 2k to Windows Server 2003. All works fine in Windows 2K but i am not able to view pages using Windows Server 2003

You have to enable the ASP.NET in the Web Server Extensions list
From Start -> Settings -> Control Panel -> Administrative Tools -> double click IIS Manager.

Go to the Web Service Extensions tab, click Active Server Pages, then press the ‘Allow’ button on the left.