I am planning of creating a application in Visual Sudio Pro 2012 in future. I want the app to run in XP, Vista, 7 and 8. So, does the app created in Visual Studio Pro will work on these OS or not?
If the application targets .Net 3.5 or 4.0, then it should be able to run on your desired operating systems (subject to having installed the framework), irrespective of the version of Windows on which it was developed. (Of course, you'd still want to test on all the platforms you're going to support)