Rather self-explanatory. Make sure the keyboard connector fits into the plug on the motherboard, otherwise you may need an adapter. Most new boards use a PS/2 connector for the keyboard. Make sure the mouse works. And choose the right kind for your system: serial or PS/2. If you like, you can get fancy "Natural Keyboards", which are basically regular keyboards that are bent in the middle. It takes a while to get used to them, but they are nice.