how to determine what windows operating systems are compatible with my application?

[jmcilhinney]

So my first question is how do I know what version of the visual basic language I'm using? What is the difference between vb.net, and vb6?

If you're using VS 2012 then you're using VB 2012, which is the 6th version of VB.NET. VB.NET and VB6 are basically different languages based on the same syntax. They have a rather different underlying architecture but the code looks very similar.

My second question is how do I determine the minimum operating system requirement, and hardware requirements for my application? Is there an easy way to analyze my program to get all the minimum requirements? I'll need to know once I'm going to make it available for download.

For a basic .NET application, you should generally just specify the .NET version. Unless you're doing something rather exotic or intensive, specific hardware requirements are all but meaningless these days. The .NET version will dictate the OS versions that are supported.

If you want to support XP then ensure that you don't use any version-specific features of later Windows versions, e.g. don't use the Windows API Code Pack, which provides a .NET API to the new features of Windows 7.

Also, if you target the Any CPU platform then your app will run in 32- or 64-bit mode depending on the OS. Under certain circumstances you will need to target the x86 platform to force the app to run in 32-bit mode for compatibility with existing 32-bit-only components, e.g. if you use an Access database.

My third question is, if it runs ok on my windows 7 system, will it run on windows 8?

You'd have to try fairly hard to make an app run on Windows 7 and not on Windows 8. There are always some areas of incompatibility but the vast majority of apps won't venture into those areas. .NET helps in this regard because you simply build against the appropriate .NET Framework and that all but guarantees that your app will work on any OS that supports that .NET version.