Both Windows 2003 and XP are on the same computer, on a different partition. So, hardware is identical, computer and the network adaptor. I use the same drivers on both Windows 2003 and Windows XP. I looked at the services, I tried to set them the same, that did not help. There are some TCP/IP optimization suggestions. I did them too but did not help. I am getting both faster speeds and not many signal loss on Win 2003. I know Windows 2003 has a newer kernel.