I\'m developing a C# .NET business application that needs to work on Windows 7, Windows 8 and Windows 8 Tablet.
The WinForms come under the category of desktop apps so any Machine with windows Pro installed , either it is a tablet or PC would run it. Tablets installed with WinRT won't support it as they run only Store apps
To answer part two of your question, splashtop has a Windows Metro Testbed that can be used on an ipad or Android tablet to remote into windows 8 and test the touch interface.
For part 2: Visual Studio 2012 has a built in simulator for testing Windows Store Apps, it provides methods to test any touch gesture and also allows for different screen resolutions and orientations.
This simulator can be used to test any application however. To launch the simulator, open "Program Files\Common Files\microsoft shared\Windows Simulator\11.0\Microsoft.Windows.Simulator.exe", alternatively search for the executable file.
Now inside the simulated environment navigate to the application you wish to test and run it.
This is not perfect but it works.
Windows 8 will still have win32, so all your applications which are win32 based example winform, C++, COM application will still run fine without recompiling. However Win32 will not be present on surface tablets, so they would not run there. You will have to recode your application using metro style which will intern use WinRT (windows runtime).
For details refer to my blog on windows 8
See, Windows 8 has 2 Versions RT/ PRO . The tablets that support RT wont run any Legacy Desktop apps(Your Winforms is a desktop App) . they would only run Windows Store Apps downloaded from Store .
You can always make a desktop version of Windows 8 app but that would run on windows 8 Pro Machines