The best way would be to have a config screen where you ask people to circle their analog stick to all extents. Store the min and max values and then you can divide the current value to get the relative position. Then when they've circled it, ask them to leave it centered for a second or two and you can see if it varies at all. It's probably best to have a fairly generous "dead zone".
Much the same thing that the drivers which come with analog pads do. It's a pain, but on a PC, I don't think you can rely on anything but manual configuration.
Much the same thing that the drivers which come with analog pads do. It's a pain, but on a PC, I don't think you can rely on anything but manual configuration.