I don't know what the Shuttle bios will allow you to do but you should be able to go in there and bump up the bus speed or fsb.
Try putting it up to 145mhz, that'll give you about 1595mhz. The xp1700 has an 11 times multiplier so...145*11=1595. That processor should be to do 1700mhz easily just watch your temps.
Oh and your ram might hold you back do you know what pc version it is?
C.