taking one out will be fine, when you put it in the new machine you may need to change the jumper on the back of the drive - you usually get three options to set the drive to, Master, Slave, and Cable Select. The jumper is a small piece of plastic with a piece of metal inside which fits onto some pins at the back of the drive, if you look carefuly at the back of the drive you should see something like MA, SL, CS (master, slave, cable select) - just put the jumper over the pins depending on where you attach the drive to in the other computer (the connector in the middle of an ide cable is slave, the one on the end is master). Cable select should allow the bios to auto detect whether it is master or slave or not, I always just set master or slave manually though.