I would complain that I lose connection hourly. Also, you tested this setup on multiple computers and multiple operating systems. As a experiment, you borrowed a friend's ethernet modem, and every thing worked properly. From my understanding, SBC has actually discontinued issuing usb modems because they were so unreliable. Refusing to swap a defective modem just shows how lazy and apathetic PacBell csr's display to their customers.
Are you sure that your phone line is not capable of higher speeds? SBC previously advertised 384-1.5/128 speeds. However, in practice, they would issue speeds of 384/128, 768/128. or 1500/128. Because of TCP/IP overhead, real speeds were 320/100, 650/100, and 1100/100. Since a lower speed was easier to establish than the maximum, PacBell could complete more installations in a given period. Almost everybody had to complain before they received higher speeds. PacBell would claim that line were unable to handle the speeds, but almost all those who requested the uncapping saw no difference in reliablity after the removal.
Once you receive an ethernet modem, you would simply connect it to your Linksys router. Then, attached cat5 networking cable from your router to your NIC in each of your computers. Get rid of that garbage Enternet software. Enter your username and password using the router's html interface and you are done. You can now turn on any of your computers and they will be connected to the Internet. One computer does not have to be on all the time to act as a server. Only the modem and router have to be turned on fulltime.