Support the staff and avoid criticizing or arguing. Communicate often with the principal and staff. I close with the quote that hangs on the door to our room. Never doubt that a small group of thoughtful, committed people can change the world. Indeed it is the only thing that ever has.
Several groups link schools with donors of used computers.
You'll find their coordinated site on the Web. Contact your local university and start a dialog. Call every few months so they don't forget you. Contact the local Macintosh and PC user groups. They are a remarkable resource for a multitude of computer matters.