Another place to check to get rid of old computers is craigslist. Look in 'Wanted'. You'll probably find a recurring post for old electronics/computers.
To be secure, just remove any hard drives and trash the rest.
You could try reformatting and reinstalling windows on the drives, just for an excercise..
Or, if you want to have some fun, take the drive apart and use the platters for skeet practice.
