You could put your old hard drive into your new computer, depending on the connection. Your new computer will surely be SATA whereas your old computer may be IDE depending on how old it is. If it is an IDE then you can get a converter for it, http://www.maplin.co.uk/sata-to-ide-convertor-36036
Setting the master/slave on your IDE is easy, just look on the print on top of your hard drive and there will be a diagram of how you set the jumpers for master and slave, follow the slave ones and you will be sorted.