Though .Net classes are vast and versatile at time you will have to resort to Win32 API calls for accomplishing certain tasks.
The following code shows a simple example of invoking a Win32 api.
The best way to use Win32 apis is to encapsulate it in a class module.
The namespace for COM interop is System.Runtime.InteropServices.
The method name should have DllImport attribute specifying the name of the dll. Here the dll is user32. Other dlls are Gdi and Kernel.