Ethernet hardware address (AKA MAC or NIC address)
The MAC or NIC address is usually a string of numbers or numbers and letters separated by colons, e.g. 00:01:02:03:04:05. This number identifies a particular computer on the network (its ethernet card) and is commonly used for tracking and security purposes. In order to obtain this number follow the instructions below:Macintosh users
Mac OS 9.x
If you have a Macintosh laptop, you can use the Apple
System Profiler tool 
. This
application comes preinstalled with most Mac Operating Systems. When
you run this tool, a window will display the hardware address of your
computer:
If you do not have this application installed, you can download it from Apple's website at http://asu.info.apple.com/swupdates.nsf/artnum/n10098
Mac OS 10.x
In Mac OS 10, you can go to the Apple menu and select About
this Mac... In the About box, you will see a
button labeled More Info. Click that, and you will
launch OS X's System Profiler.
Once in the Profiler, you can select Network, which will display the Ethernet Address.
Windows users
Windows 95/98 users:
1. If you are running Windows 95/98, type “winipcfg” at the Run prompt in the Start menu.
2. This will open an application called “IP Configuration”, which will display the hardware address of your laptop.
Windows 2000 users:
If you are running Windows 2000, you can use the Command Prompt to locate the hardware address of your laptop. The Command Prompt is usually located in the Accessories folder within the Programs folder available from the Start menu. At this prompt type "ipconfig/all"
Windows XP users:
You can find the information in much the same way. Just type "ipconfig/all" into the command prompt. You can also reach the command prompt by going to the Start menu, selecting Run..., and typing "cmd".
Linux users
Different Linux versions and distributions can vary widely, but what follows is one method for determining a hardware address. If you are using a graphical enviroment such as KDE or GNOME, launch a command shell (If you do not use a GUI, this will not be necessary). In the command line, type "/sbin/ifconfig". Below is an example of the listing that should follow. The hardware address should be listed as HWaddr.
