I use a router (D-Link DI-704P) for the simple fact that I don't have to leave one computer always on for any of my computers to get internet or printer access. With a router all the bandwidth is shared anyway, so you'll only notice a decrease in speed when one of the other computers is downloading lots of stuff, but then again pretty much all forms of home networking shares bandwidth like that.
You kinda lost me as to why you'd need the second phone line though, for one of those 3-com telephone networking kits?
"Driving is like a narcotic, an addiction that can take over lives. It ruins people, breaks families apart, and even kills. Itís habit that needs to be fueled. Time, money, rationality, sweat, knuckle skin, and anyone who disapproves are of little importance to a driver, and are often overlooked. Hi, Iím Nelson, and Iím a drivaholic."