A common question is, "How far away from the computer can the touchmonitor be?" The answer, of course, is, "It depends."
Serial cables: The spec on serial cable length is something like, "As far as it can be run without degrading signal quality significantly." In practice, several of our customers have run serial cables 200 to 400 feet without problems.
USB cables: The spec on USB is no more than five meters between powered hubs, five hubs max. So by default you can go approximately 15 feet, and with a single powered hub you can go approximately 30 feet. Powered hubs are a common item, widely available. To go longer distances, you might want to consider a third party USB extender.
Video cables: Six feet is the de facto standard for video cables; longer cable length degrades the video quality unless special cables are used. There are many companies that provide special cables to help you extend your reach 50 feet or more. Video amplifiers are also available from third parties.