Master/Slave things are confusing most of the time.
It depends entirely on the IDE bus you add it to (these are IDE, I assume, with a 40pin connector) and what else is on that bus.
If your primary IDE has a HDD on the end (typically for the master) but nothing on the middle connector (typically for the slave) then you could set your drive to Slave and put it there.
As I said, it depends entirely on the config within the PC.
Also, you may need to review the settings in the BIOS - the boot order may end up looking for your drive after you remove it or you may have to move your drive up in priority.