You could try taking a look at:
http://www.computeraid.org/home.htm
From their FAQ:
Are the hard drives wiped, and if yes, to what standard?
Yes. All data and programs are completely removed. All hard disks are reformatted as standard and at no cost to you. A full unrecoverable multiple disk wipe to Ministry of Defence standards is also available.
Does Computer Aid International collect donated computers?
Yes, Computer Aid has a limited collection facility. Please call for details.
Does Computer Aid International accept full legal liabilities?
Yes. We accept full legal liabily for any donated equipment from the time it is received by us: i.e. covering any subsequent damage or injury arising from the malfunctioning of the covered technical assets.
Who will benefit from computer donations?
Schools and community organisations in some of the poorest countries in the world.
What type of computers does Computer Aid International accept?
We accept IBM compatible computers of Pentium specification (and equivalents).
Does Computer Aid International accept peripheral equipment?
Yes. We take printers, colour monitors, modems, cables, and any other peripheral devices.
Are Computer Aid International willing to publicise our donation?
Yes. We will be happy to work with you on joint press and other media publicity.
What are the costs for us?
We may ask for a small contribution towards collection costs. Please call us for details.
They seem to have all the bases covered legally.