Helping a young child, or a child with motor-skill issues use the computer may not require the purchase of an expensive touch-screen monitor.
TeachTown has been undergoing field testing at the San Diego Unified School District for about 6 months. About a dozen of their “mentor” teachers are using TeachTown: Basics in their classrooms.
The teachers there told us about a simple but clever method of helping out a child who does not know how to use the mouse. It requires that the teacher or parent sit with the child (which is typical when working with a young child or a child that has OT issues.) Essentially, you can let the child touch the screen of a regular monitor. The facilitator (teacher or parent) moves the mouse to the position where the child touched and clicks the mouse. [You can of course use this method with any other software or interactive web-site.]
Once your child gets used to the contingent reinforcement of interacting with the computer, you can eventually work on transitioning them to a mouse or other assistive technology device. I also found a good website that sells computers and mice for little kids: http://www.kid-computers.com/. If anyone tries out one of these mice for younger kids, please feel free to send me a review of your experiences!