I recently installed a hardware upgrade on my email server and was forced to reboot the machine.  [The machine is a year old or so, Socket 754 AMD64 processor, MSI K8T NEO-FIS2R motherboard.]  After the machine came back up, I noticed that the NIC driver (Realtek 8110S integrated NIC) did not load.  This had been working for the past 6 months or so (ever since I installed Windows Server 2003 on the machine) and has been used in a production environment without incident ...

Perplexed, I went rooting around for a driver for this NIC that supports Windows Server 2003 and could not find one specific to that operating system.  How in the world did I get it to work before ???

To make a long story short, I discovered that I had previously installed the Realtek 8169 driver, despite the warning that this driver did not match the hardware.  Installing this driver did the trick ...