It is a myth that the primary master HAS to be your system drive (although the installer of the system may moan) but you can boot from any one of these devices on power on.
If you see what channels you have occupied (you may find both your drives are masters (hard drive as primary master and cd drive as secondary master)) In this case you would set the new hard drive to slave and put it on any channel (i'd suggest secondary to improve speed)
If you have SATA hard drives and CDROM drives this will free up your PATA channels and allow you more devices. I personally prefer PATA as its a bit more established and runs solidly but for faster speed go for SATA.
It's depend on you.If you want to start your computer with old hdd then you have to set the jumper on back side of your hdd in master and the new hdd jumper set to the slave.
GLC T - [SIZE=-1] " Responsibility is not mindless obedience to rule. True responsibility is using the mind you were given to make your own decisions, not slavishly adhering to the choices others would make for you."[/SIZE]