I have a D-Link DGE-528 1Gb/s network card running on Debian Sarge 3.1 (Kernel 2.6).

The card(driver?) does not support PHY or MII, therefore 'ethtool' and 'mii-tool' will not work, so I cannot determine a way to see what speed the NIC is link negotiating at.

I need to know if the card is running at full duplex 1Gb/s.

Does anyone know of any other tool that I can use apart from the aforementioned well-known ones?

Your NIC will only operate and the duplex and speed of the device that it is connected to. For instance, if you have a 1gbit NIC and are connected to a modern cable modem for Internet access, then that NIC will only run at 100 mbps, which is the maximum the ethernet port on most modern cable modems can support.

On the other hand, I have a 1gbit Zycel switch on my network at home and all my machines have 1Gbit NICs in them and communicate very nicely with each other. However, the connection between the 1 gbit switch and the router is only running at a max of 100mbps since that is all the ethernet port on the router can support.

That info probably also is in your /var/log/messages as soon as you boot your computer.
When my computer starts up, it logs the following message:

Apr 10 22:09:16 xxxxx kernel: eth0: Media Link On 100mbps full-duplex

The PC is connected to a 1Gb/s switch, and there are WinXP PC's also connected to this switch which do report they are connected at full speed.

@pk21
Thanks, I do get this message in the logs; but I wasn't sure if that was just stated what max speed the card supports not actually the speed it's connected at. Am I wrong?