The Mesmic 2125 accelerometer (http://www.parallax.com/Portals/0/Downloads/docs/prod/acc/memsickit.pdf) outputs a variable-width pulse rather than an analog voltage. At 0G the output pulse is 5000 microseconds high and each 1G would be a change of 1250 microseconds. A pulse of 3750 microseconds would be -1G and 6250 microseconds would be +1G. The code for that would be something like this:
int accel = pulseIn(MemsicPin);
int angle = map(accel, 3750, 6250, 0, 180); // map -1G through +1G to 0 through 180
myServo.write(angle);