For whatever reason lets assume you find yourself on a Windows machine and you need to obtain the MAC address of its network adapter. Do the following.
Go to Start -> Run which will bring up a text box. In this box type cmd. A command prompt will appear.
Type this is the terminal.
ipconfig /all
A lot of information will fly by but the MAC address is labeled Physical Address. The number is 6 pairs of hexidecimal numbers separated by dashes. It will look like this.
Physical Address . . . . . . . . . : a1-b2-c3-d4-e5-f6
If the machine has more than one network adapter (wired and wireless), then you will see an address for each one.
This will work with Windows 2000/XP/Vista.