there are two ways...
either get on the M4 (great western highway) and follow it all the way to bathurst
but the best way for a northern beaches person... make your way to Bells line of Road... head through richmond and windsor.... and follow the signs to lithgow. Once in lithgow you end up turning right onto the great western highway anyway... again just follow the signs to bathurst.
once you're in bathurst you'll go through Raglan and Kelso, then over a bridge with shitloads of street lights on either side, then past a big field on your left. After the field turn left at the first set of lights (there'll be a sign saying "charles sturt uni") this is Bentinik st. Follow this street all the way to the end, you'll go up a really steep hill and past St Stannislaus college... go back down the hill and at the give way sign go left, then walla!
take the first right into the uni...follow the signs to the information center if you're after a tour...
hope that helped