Is GDI+ faster than GDI?
The answer depends on what you are trying to accomplish. Currently, based on my experience, GDI+ is not faster than GDI. Even when compared in Windows XP, GDI outperforms GDI+. If raw performance is necessary, you may have to use GDI. However, GDI+ does provide some powerful features, and it should speed up later as new optimized hardware is developed.
Do I have to use GDI+ to draw in the .NET Framework or can I use GDI?
GDI+ is the only API provided through the .NET Framework for graphics. It is possible to write unmanaged code to use GDI if it is important to do so. However, GDI+ is the way to draw in the future, and your efforts should focus toward using it.