Spoof MAC address in Windows or gnu/linux

start -> run -> regedit
make a backup, if you want.
goto:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}

look through the list of subkeys (0000, 0001, etc)
DriverDesc keyword will tell you which network adapter. For example, “NVIDIA nForce Networking Controller”
when you find it, right click and add -> new -> string value

new keyword:

Value Name: = NetworkAddress
Value Data: = your new MAC, with no space or : For example, 0019DB71C830

then type:

ipconfig /release
ipconfig /renew
ipconfig /all   (to verify the new mac took)

Now your a l33t Winblows H4|<3r! If you want to go back to your hardware MAC, remove the NetworkAddress key and restart the interface. FYI, in gnu/linux follow these simple steps to change your MAC address

ifconfig eth0 hw ether 00:19:DB:71:C8:30

if you get this error

SIOCSIFHWADDR: Device or resource busy - you may need to down the interface

do this

ifconfig eth0 down

and try to change the MAC again.