Where I work we used to try and give away shed loads of I.T. equipment, nearly all Dell, and all in good working order. It really is difficult as charity shops didn't want all of it, they make take some items. By the time you have driven round a few shops trying to get rid of it, it has cost you time. So we now hire an electrical waste cage and just scrap the lot.
Some do - I think the British Heart Foundation do, but if not, look up the number for your local Women's Refuge and offer it to them - they are keen on anything they can use or re-deploy.
The most difficult thing to do is give something away, much easier would be to advertise it for sale in 'full working order' for 3 quid and someone will grab it as a bargain