If this is new construction and pre-drywall, your friend would be well advised to run Cat5 or higher grade cabling throughout his house, and then home run everything to a central point (like a basement as bazookatone pointed out). Where is the CATV/SAT and the phone line coming into the house? Wherever that is, perhaps that would be the best place to centralize everything.
The DSL will come over the normal phone line and then into a DSL modem/router. If your friend only has phone connections in every room, then he has to move that DSL router to whatever room he wants to work in. If the DSL router were to be connected to a hub/switch which also serviced every room with Cat5 connections, then your friend would only need to plug his laptop/PC into the nearest available network/RJ45 port. He could also have multiple computers using the DSL line at the same time. Being forward thinking, your friend could then plug in some of the newer A/V Internet-ready equipment into a port, or home appliances (e.g. refrigerator), etc. Even without DSL as a consideration, however, with new construction it would be worth running all the network cabling so that you could at least have a home network for gaming, servers, or whatever without running long cables across the carpet.
