As far as the POS, I also came to them with this problem. They do not have this issue with any other clients, however we seem to be one of the first to be using an all Windows 7 system. The only "time-out" that the POS has is it's database which is set to 12hours of idle time. Other then that we can not find any other problem.
I will attempt to get new drivers and test them out, as all the PC's have different hardware in them, and they all have the same problem, i can assume if it IS a driver issue, that it would have to be the Server NIC driver.