You'll need a PIC with onboard A/D to use ADCIN. This works on an F876.

Code:
DEFINE  OSC 4
DEFINE	ADC_BITS 8      ' Set number of bits in result
DEFINE	ADC_CLOCK 2     ' Set clock source (3=rc)
DEFINE	ADC_SAMPLEUS 50 ' Set sampling time in uS
SVO_POS VAR BYTE

    ' 90 deg horn rotation (adjust for servo)
    'LEFT    CON 100       ' Left position 1mS
    'RIGHT   CON 200       ' Right position 2mS

    ' 180 deg horn rotation (adjust for servo)
    LEFT    CON 70         ' Left position 0.70mS
    RIGHT   CON 240        ' Right position 2.4mS

    TRISA = %00001001 ' RA0 = A/D input
    ADCON1.7 = 0      ' RA.3 = +Vref, Set PORTA analog and left justify result
    LOW 0             ' Setup RB0 for high-going pulseout

Loop:
    ADCIN 0,SVO_POS   ' Read A/D channel
    IF SVO_POS < LEFT THEN SVO_POS = LEFT
    IF SVO_POS > RIGHT THEN SVO_POS = RIGHT
    PULSOUT 0,SVO_POS ' Move servo
    PAUSE 15            ' ~60Hz update-rate
    GOTO Loop         ' Forever