For the case fans I would check the width from one side to another and buy one the same size, just make sure the new one has the same plug on the end.
For the CPU one you should check the connection to the motherboard and more importantly, the CPU socket it is for. You can usually find out the socket by looking up the model of your CPU on a search engine and then all you need to do is find a cooler that fits that socket.
Just make sure that you buy fans and a CPU cooler that have good performance and are quiet. I'd get one from a big brand such as Antec/Coolermaster and many others. Stay away from the no-name/strange brand ones.
