Due to San Andreas being ported to PC from the PS2 version, the control system has been changed a lot. Unfortunately, the replacement isn't too great for PC's using Joypads and people used to the PS2 or Xbox versions will never get the same feel from this system as the exact console controls can't be replicated.
GTA IV doesn't have this problem, however. XInput, an API for Xbox360 controllers published by Microsoft as part of DirectX, is used to handle joypad input, and it works pretty well. The fact it only worked for Xbox360 pads influenced a user-made patch (provided with GInput) which allows configuration of XInput to work with pretty much any joypad on the market, so I decided it would be a good idea to use this to enhance the control system in GTASA.
So GInput knocks out GTASA's current DirectInput system in favour of XInput. It also replaces keyboard key names with PS2 or Xbox button textures, making the controls feel just like the console versions. As it directly processes the controls based on what joypad buttons are pressed, skipping the menu configuration, all the controls work the same as the console versions. Wheras before this was not possible as SA would stop the same buttons having multiple uses.