you can download SMAC at
http://www.klcconsulting.net/smac
Here are the steps for changing MAC addresses on Win 2000 & XP:
1. Install and run SMAC
2. select the network adapters that you want to change the MAC addresses
3. type in the new MAC addresses
4. disable and re-enable your network adapter(s) or reboot your system.
That's all. You will see a brand new MAC for your network adapters!