If I remove the DEFINEs usually associated with the ADCIN function:

Code:
'DEFINE ADC_BITS      10     ; Set number of bits in result
'DEFINE ADC_SAMPLEUS  50     ; Set sampling time in uS (was 5)
'DEFINE ADC_CLOCK     3      ; Set clock source (3=rc)
and use Fosc/8 as the timer:

Code:
ADCON1    = %00010000       ; Left-justified results in 8-bits; Fosc/8 as timer
Then I get 0-255. If I do the same for 10-bit resolution, though, I now get 1-1023.