Much of what your talking about is possible using DirectInput. Many games use the mouse as a controller. Im not sure how DI would handle additional non standard mouse buttons tho. The real problem is theres absolutely no restrictions. Theres nothing saying that logitech cant make a 35 button mouse if they wanted to. Theres no real method that windows could use to standardize mice. WM_#BUTTONDOWN maybe? I dont see any reason to even try. Windows already supports 3 button mice and wheel buttons. If you need any more control use the keyboard.