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Thanks for the suggestion about the PCI cards.
ACtheTROLL and ChuckFickens - I don't understand what you mean by "wireless really isn't suitable for running several computers at the same time from it" and "beyond one ... they'll interfere with each other". We currently use 13 laptops with wireless connections in one room and there is no problem whatsoever. Are wireless dongles or wireless PCI cards any different?
Also, at home there are seven wireless networks within range and again there is no problem with interference.
The point about speed is valid, but does it really matter, when the speed of the broadband is at best 8Mbps, 54 Mbps with wireless is more than adequate. I use wireless at home and have no complaints about the speed.
What is Homeplug?