Should I use WPF instead of ASP.NET

If you are considering building a Web Application and want to look at the latest technology to build this, consider using Silverlight(similar to WPF). WPF is generally preferred to build client applications(WinForms). You may also use just the ASP.NET(without the use of Silverlight) to build the WebSite/Web Application. PLease be informed that Silverlight/ WPF is the the technology to build the UI partof the application. And in any case you have to use ASP.NET for building Web Applications/Websites. Silverlight applications cannot be build in isolation.