1) what should i spray it with to kill the weeds - Roundup Biactive, it will kill all weeds and the roots too. Spray at least 7 - 10 days before digging up your old driveway.
anything i can do to stop the gravel moving? - I am planning doing my own driveway at the moment and have been advised not to put on the stone too deep as this results in deep tyre tracks etc. Its best to put on 25mm of dust (the same colour as the final stone), roll in well, and then apply 25mm of stone on top of this.
Just seen a beautiful driveway this evening that was done with light gold stone. Manor Stone supply it [broken link removed] but I think it is quite expensive .