Combined pedals means that the controller uses the same joystick axis for
the gas and the brake. The top half of the axis is used as the gas and the
bottom half of the axis is used as the brake. The disadvantage to this is
that you can't use the gas and brake at the same time. The separate option
uses the Y-axis for the gas and the X-axis of the second joystick for the
brake (or the other way around). The advantage is that you can use the gas
and brake at the same time.
Note that only some games support separate pedals. My guess would be to
always use the separate option if the game supports it.
--
Kevin
(Remove the "x-" prefix from my address in order to reply via email)