Tyler is right. Companies dispose of computers all the time that are more than fast enough to get this job done. Since they have to pay to dispose/recycle, you can easily pick them up for free.
We offload a bunch ourselves each cycle. We offer them up to employees, but only so many are in need of a new computer so inevitably several just get junked. We're talking 2+ GHz dual-cores at this point.
Just ask around.