This program lets you spoof your MAC address and set the one you'd like. You can set a random address or start by known OIDs provided by an internal database. This works on wireless interfaces too.

Did you ever get bored with your old MAC address If you did, this is the solution! Mac MakeUp let's you change the MAC address of any of the interfaces present on your Windows 2000/XP/2003/Vista box.
Sometimes this is referred as MAC address spoofing.
You can choose a new address of your choice, or get the new one with the help of the tool, which sets the OID part according to your preference.

* Enable routing features Makes your PC act as a router, forwarding packets from one interface to the other. Useful if you intend to use your laptop to route between wireless and wired networks
* Allow user raw access to sockets By default only admins can access raw sockets. This lets you override this setting
* Enable address mask reply (ICMP) Lets your station respond to subnet mask ICMP requests
* Accept ICMP Redirect Lets your station accept ICMP redirections
* Disable hw acceleration Disables task offloading to your network adapter (IP, IPSEC, ...)
* Enable selective acknowledge (SACK) See RFC 2018
* TIME_Wait delay The time a connection stays in Time wait state
* Max number of TCP connections Maximum number of TCP connections
* Max user port This controls the maximum port number used when an application requests any available user port from the system
* Default TTL This controls the maximum port number used when an application requests any available user port from the system
* ARP cache life (unreferenced) ARP cache life in seconds for unreferenced entries
* ARP cache life (referenced) ARP cache life in seconds for referenced entries
* ARP checks for own IP This controls the number of times that the computer sends a gratuitous ARP for its own IP address(es) while initializing
* Source routed packets behaviour 0: Route All - 1 Do not route - 2 Drop incoming
* Multicast support 0: No multicast support - 1: Send multicast - 2: Send and receive multicast

The license of this software is Freeware, you can free download and free use this ip utility software.