I'm using the G25 clutch and throttle pedals as rudder pedals, the brake pedal as left and right brake pedals and the wheel as throttle.
The trick (and only way) to getting the pedals to report as a single axis and be able to use them in FSX, is using a joystick emulator called PPJoy and a game controller scripting program called GlovePIE. Both are free.
I installed both, then wrote a script that would take the axes of the G25 to move the axes of PPJoy, which can then be assigned in FSX. (Note that your axes will probably be named differently, so you need to change those before it'll work).
This uses the G25 throttle and clutch pedals, which my system recognizes as Joystick2.dial and Joystick2.y, to move my virtual PPJoy joystick.
//X axis = Clutch & Throttle pedal
PPJoy1.Analog0 = 0.5*Joystick2.dial - 0.5*Joystick2.y
Likewise, I can also hook up my brake pedal to be reported as 2 PPJoy pedals, so I can configre those as Brake Left and Brake Right in FSX
//Slider 1 & X Rotation -> Brake pedal
PPJoy1.Analog4 = Joystick2.rz
PPJoy1.Analog6 = Joystick2.rz
And this is how I set up my wheel. Note the 1.04 value! Since the G25 moves back a few milimeters when you push it to its lock due to the FFB, it's impossible to leave the value at 100%, so I multiplied it a little bit.
//Z Rotation -> Steering wheel
PPJoy1.Analog2 = 1.04*Joystick2.x
Then... to make my life even easier, I just created a shortcut on my desktop that would run my GlovePIE script and then start up FSX, and filled in the following under Target:
"E:\Program Files\GlovePIE\GlovePIE.exe" -SCRIPTNAME /r:"C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\fsx.exe"