There is such a thing as cascading old/unwanted IT equipment to Africa - try turingtrust.co.uk/Africa, there will be others. Zac's caution is not entirely unreasonable but thoroughly removing data from a hard drive is not so very difficult. All you need to do is properly re-format the hard drive in/from the old computer (perhaps twice over for good measure) - to do this it may be necessary to remove it, format it separately, and then reinstall it (or simply donate the stuff "in bits"), if you cannot do this yourself, you should have no difficulty finding someone who can. At that stage the disk should be effectively blank - do not rely on simple deletion, that leaves much of the data still recoverable by those who are sufficiently knowledgeable. Do not pass the machine (or rather the hard drive) on without formatting first