Results of a NIOSH study suggest that taking short rest breaks within every hour (three 30 second, and one 3 minute per hour - at 15 minute intervals) in addition to normal 15 minute morning/afternoon breaks "can facilitate performance and forestall the development of discomfort in repetitive VDT (video display terminal) work." In the study, users who took the additional breaks actually had a higher keystroke count than the control group, which did not take the additional breaks.
R. Henning, S. Alteras, P. Jacques, G. Kissel, A. Sullivan, University of Connecticut.
NIOSH's # is 1 800 356 4674. This is a general information number. They also can provide some additional information about ergonomics.
You may want to request to be placed on a mailing list of training programs they offer.