Check out the PWM function in ARC. Set it for one of the digital ports and put a voltmeter on the signal and ground, play with the slider and look at what happens

It wont power much, the signal pin on the EZB doesn't supply much current at all. It's enough for LEDs but that's about it.

100ma is the most it can power Avg LED is 20ma

I actually would like to use the voltage output to emulate a joystick control for a wheelchair. The wheelchair requires 2x lines that can be varied from 0-5v for the forward/backward and left/right motions.

I should have come right out and said this but i thought the LED example would yeild the same result.

Could a H-Bridge achieve this? You can use the PWM controls with the 4 digital ports of a HBridge to vary the speed of the motors attached to it. For instance D0 to D3, PWM of 20% on D0 and D2 would make it move forwards at 20% speed, using a 5V supply to the HBridge would give that 0-5v on the HBridge output pin. You may only need to use 2 digital ports if you only need 2 0-5v lines.

Also, my Darlington Transistor circuits dim the lamps when PWM is used on them, the supply to the lamp is not from the signal wire. I'm not entirely sure how this works but it would be worth looking in to a little more.