How old is the computer? If it isn't ancient, donate it to a local charity, particularly one that helps people get back into the workspace. Be sure to reformat the hard drive to remove the old data.

Go to freecycle and post an ad for it on there, you'll find someone will want to take it off your hands.

About reformatting: You need to do this a lot. It's recommended that you do it at least 6 times. But there's software out there that can recover information even if you reformat a dozen times. They probably won't be able to get everything, but if people get the right bit of info - like your bank account number - then it doesn't matter that that's all they got. There are programs available that will overwrite your data to make it more difficult to recover. I've heard of a few but can only remember one called Eraser. Don't know if it's any good. And don't believe all that stuff about putting magnets on it. There's a magnet in the hard drive that makes it work. You'd have to have a really big strong magnet to mess up a drive.