What are the exact differences between a web program and a stand-along program, programming wise?

Hi, I have over 10 years of experience developing Windows applications. I need to know exactly what the difference is between this and creating a program on the web. I have SOME background on small projects in ASP.NET; however, is there a site that lists EXPLICITLY what I need to learn in order to be able to dive right into web development and make sure I haven’t “forgotten” anything. Thanks!!!!