I do not know why you are not connecting at 1Gbps. As you probably expected, this should just work. You already have the latest driver for the Intel(R) Ethernet adapter, so you might want to take a look at the nVidia end to make sure everything is up to date.
Is the system with the nVidia connection running the latest BIOS and does the nVidia network connection have the latest drivers? If not, you might try updating the files on the nVidia end to see if that fixes the connection.
I do not know of any driver or hardware problem with the Intel® Gigabit CT Desktop Adapter. I tried hooking one up back to back with another machine, and I get a 1Gbps connection with the default auto negotiation settings. Unfortunately, I do not have a system with an nVidia NIC that I can try as a link partner.
Would you mind providing more details? I want to make sure I am researching the right adapter. What does Windows Device Manager call your adapter, Intel® Gigabit CT Desktop Adapter or Intel® PRO/1000 CT Network Connection?
What are the driver provider, date, and version on the driver tab? What is the name of driver (the ".sys") file? The details button on the driver tab will show the name of the driver file.
On the device manager details tab, what are the hardware ids?
What motherboard and which slot do you have the adapter plugged into? (Computer system make & model might give me motherboard information if you do not have it.)
Similar details about the system with the nVidia NIC would be helpful. If I can find something similar as a link partner, maybe I can see the same connection speed issue you are seeing.
I did find a Server with a built in NVIDIA nFORCE Networking Controller. Making a back-to-back 1Gbps connection was no problem using the default "auto negotiation" setting.
You might try running the diagnostic tests on your adapter and a different Ethernet cable. Yes, I know the cable worked with the other 2 connections, but I do not see an obvious answer to your problem.
It shows up as "Intel(R) Gigabit CT Desktop Adapter" (even in the device manager), but the adapter says intel pro1000ct desktop adapter. This is why I thought maybe it was a driver issue but I can't find any drivers for the pro1000ct. The default win7 driver was "Gigabit CT" and even when I updated the driver with the one I posted earlier in the thread, it still comes up as the same thing.
Driver provider Intel
Driver date 12/4/2009
Driver version 126.96.36.199
Motherboard is Intel dg43nb, it's got 2 PCI-E slots and I've tried both (Maybe there's a setting in the BIOS that needs to be changed? I just thought of that but not sure where to begin looking)
2nd PC is:
NVIDIA nForce Networking Controller (onboard, can't remember what motherboard, don't think I have any boxes left and I don't want to take it apart to find out)
and just for the hell of it, the third computer with a separate ethernet cord is:
Intel 82567v-2 gigabit network connection
I ran the diagnostics last night, everything passed except the connection test because I had to force 100Mb:
Cannot run the connection test.
TCP/IP protocol not configured.
To run this test, this connection must
be configured to use the TCP/IP protocol.
This adapter is configured to force the
speed to a low speed.