If MAC address spoofing is your only requirement, you'll find the steps to perform this manually, here:
http://www.windowsreference.com/networking/how-to-change-mac-address-in-windows-registry/If you are unable to change MAC address, following may provide guidance:
http://www.klcconsulting.net/smac/smac_faq.htm#Why%20can%27t%20I%20get%20SMAC%20to%20work?Hope this helps.
Warm regards,
Sarang
