1. 在 HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}\0000、0001、0002等主键下，查找DriverDesc，内容为你要修改的网卡的描述，如“Realtek RTL8029(AS)-based PCI Ethernet Adapter”。
2. 如果在0001下找到了1中的DriverDesc,在其下，添加一个字符串，命名为NetworkAddress，其值设为你要的MAC地址（注意地址还是连续写）。如：00E0DDE0E0E0。
3. 然后到其下Ndi\params中添加一项名为NetworkAddress的主键，在该主键下添加名为default的字符串，其值是你要设的MAC地址，要连续写，如：000000000000。（实际上这只是设置在后面提到的高级属性中的“初始值”，实际使用的MAC地址还是取决于在第2点中提到的NetworkAddress参数，这个参数一旦设置后，以后高级属性中的值就是NetworkAddress给出的值而非default给出的了。）
4. 在NetworkAddress的主键下继续添加名为ParamDesc的字符串，其作用为指定NetworkAddress主键的描述，其值可自己命名，如“Network Address”，这样在网卡的高级属性中就会出现Network Address选项，就是你刚在注册表中加的新项NetworkAddress，以后只要在此修改MAC地址就可以了。继续添加名为Optional的字符串，其值设为“1”，则以后当你在网卡的高级属性中选择Network Address项时，右边会出现“不存在”选项。
5. 重新启动你的计算机，打开网络邻居的属性，双击相应网卡项会发现有一个Network Address的高级设置项，可以用来直接修改MAC地址或恢复原来的地址(选中不存在)。

For Windows 2000/XP

Method 1:
This is depending on the type of Network Interface Card (NIC) you have. If you have a card that doesn’t support Clone MAC address, then you have to go to second method.
a) Go to Start->Settings->Control Panel and double click on Network and Dial-up Connections.
b) Right click on the NIC you want to change the MAC address and click on properties.
c) Under "General" tab, click on the "Configure" button
d) Click on "Advanced" tab
e) Under "Property section", you should see an item called "Network Address" or "Locally Administered Address", click on it.
f) On the right side, under "Value", type in the New MAC address you want to assign to your NIC. Usually this value is entered without the "-" between the MAC address numbers.
g) Goto command prompt and type in "ipconfig /all" or "net config rdr" to verify the changes. If the changes are not materialized, then use the second method.
h) If successful, reboot your system.

Method 2:
This should work on all Windows 2000/XP systems
a) Go to Start -> Run, type "regedt32" to start registry editor. Do not use "Regedit".
b) Go to "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}". Double click on it to expand the tree. The subkeys are 4-digit numbers, which represent particular network adapters. You should see it starts with 0000, then 0001, 0002, 0003 and so on.
c) Find the interface you want by searching for the proper "DriverDesc" key.
d) Edit, or add, the string key "NetworkAddress" (has the data type "REG_SZ") to contain the new MAC address.
e) Disable then re-enable the network interface that you changed (or reboot the system).

Method 3:
Use the program Etherchange from http://ntsecurity.nu/toolbox/etherchange/