Even Windows can be used to change your MAC Address. And, I am not asking you to purchase commercial programs like SMAC to accomplish this. Commercial packages simply fiddle with the registry settings to spoof MAC address on any interface.
Armed with this information, you are ready for this MAC spoofing exercise. To change the MAC for your wireless card in Windows, you will have to edit the Windows Registry manually.
Open regedit and navigate to HKLM\SYSTEM\CurrentControlSet\Control\Class. Once there, start looking through the entries for your card. The key includes a description of your card, so it shouldn’t be too difficult to find. Once you have found your card, create a new key named NetworkAddress of type REG_SZ. Insert your desired 12-digit MAC address. You might be able to get your card to recognize its new MAC simply by disabling and re-enabling it. Other times, a reboot will be required. If you want to revert to your original MAC, delete the NetworkAddress key.
But, what’s the entire fun in spoofing MAC addresses? True, normally you would never end up doing this. But, it comes handy in situation when you want to use wireless networks, which grant access to the clients based on their MAC address.
This post is being written by breaking into a SOHO wireless network, running in my neighborhood which offered Internet access. This must have given a fair idea about what MAC address spoofing can be used for 🙂 !
Scribbles of a Chaotic Mind 
Wow, I always thought that its not easy to such a stuff.. I ahven’t got xp, but I just took a look into vista’s regedit, and I can see the network card, will definitely try that out..