So I am looking at this page here http://arduino.cc/en/Main/ArduinoBoardMega2560 which has pictures of several revisions of the Mega2560 and discusses their differences.
So I look at the top four pictures at the top of that web page closely and see that my Mega2560 has the mostly blue back with the white circle design, and doesn't have the extra pin next to the AREF pin, so it is probably the first version of the Mega2560, BUT the chip nearest to the USB socket isn't turned diagonally the way it is depicted in the photo, so I am uncertain....
So then I read this page http://arduino.cc/en/Hacking/DFUProgramming8U2 which talks about identifying the driver for the Atmega8U2 chip as follows:
"Check whether you need to update the firmware
The Arduino Uno and Mega 2560 have been shipping with the updated (rev. 0001) version of the ATmega8U2 firmware since around May, 2011. To check which version of the firmware is on your board, connect it to your computer and follow the directions for your operating system:
Windows: locate the board in the Device Manager (it should be under Ports), right click on it and select "Properties"; in the resulting dialog, click on "driver details" in the "driver" tab. In one the properties, you should the VID, PID, and the revision number. "
which says that the driver is 6.1.7601 17614. which doesn't look anything like rev.0001 at all.
And there isn't any "VID or PID" or revision number. Not behind the "Details" button on the "Driver" tab and not behind the "Details" tab or any of its properties either.
So how do I tell if the ATmega8U2 firmware needs to be updated ?