Apple made two G4 17 inch 1.67Mhz Powerbooks - one's a higher spec than the other and tends to be more sought after than the other and consequently goes for a higher price. The difference between them is principally a higher native screen resolution - 1680 x 1050 as opposed to 1440 x 900, a double/dual layer superdrive and uses faster RAM.

The fact yours comes with a 100Gb HD suggests it's the lower spec of the two as the higher spec one came with a 120Gb HD. Check the model numbers - the high spec one is A1139/Powerbook 5,9 and the lower spec one A1107/Powerbook 5,7.

Cheers