Fire up VS, start new Windows Application. Open the properties sheet, add the .png file as a resource (in this example: glider.png ). From hereon, you can access the resource as a Bitmap file as WindowsFormsApplication10.Properties.Resources.glider
Code for using it as an application icon:
public Form1()
{
InitializeComponent();
Bitmap bmp = WindowsFormsApplication10.Properties.Resources.glider;
this.Icon = Icon.FromHandle(bmp.GetHicon());
}