"How are ASP and ASP.NET different?"
ASP was Microsoft's original server-side web programming language, based on their earlier Visual BASIC language. ASP.NET is part of Microsoft's new family of ".NET" programming languages, which are thoroughly object-oriented and substantially different from what went before. Since Microsoft strongly recommends ASP.NET over ASP, I do not recommend starting new projects in ASP.
Bear in mind that all server-side dynamic web programming languages are the same as far as the end user is concerned. That's because what ultimately reaches the web browser is just HTML anyway. That means you can build your site in PHP (which is available for free server operating systems like Linux) and reach just as many people as you would with an ASP.NET site. So use the language that works best for you and your client.
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