If you are attempting to change the en0 address on a Macintosh machine you can try the following
sudo ifconfig en0 lladdr 11:22:33:44:55:66
Or
sudo ifconfig en0 ether 11:22:33:44:55:66
The address you choose is up to you. Your MAC address will be reset on reboot.
If you want to test to see if the change took place you could try one of the following commands.
netstat -I en0 | egrep -o '([[:xdigit:]]{1,2}:){5}[[:xdigit:]]{1,2}'
ifconfig en0 | egrep -o '([[:xdigit:]]{1,2}:){5}[[:xdigit:]]{1,2}'
ifconfig | sed -n '/en0\:/,/status\:/p' | grep "ether" | sed "s:ether::g" | sed "s:[[:space:]]::g"
NOTE: 'egrep -o' works like 'grep -o -E'
If you want to switch back to your original MAC address prior to reboot you can obtain your original MAC address and switch the MAC address back with the following steps.
STEP 1
system_profiler SPNetworkDataType | awk '$2 == "Ethernet", $1 == "MAC"' | awk '$1 == "Ethernet:", $1 == "MAC"' | egrep -o '([[:xdigit:]]{1,2}:){5}[[:xdigit:]]{1,2}'
STEP 2
sudo ifconfig en0 ether "YOUR ORIGINAL MAC ADDRESS OBTAINED BY STEP 1"
STEP 3
sudo ifconfig en0 down
STEP 4
sudo ifconfig en0 up
oops I did not see that the question was specific to Windows prior to post. – E1Suave – 2012-04-20T18:53:42.660