Change MAC Address

You don't. Do a google search and see http://en.wikipedia.org/wiki/MAC_address for example

Some routers let you spoof a MAC address: this is useful if your ISP (usually when it's cable) will only accept one MAC address, so you set the router to the address of one of your computers (so that you can bypass the router if necessary). However in the computers themselves the MAC address is set in hardware and is not changeable (which is the point - every device, ethernet card, wificard, router, standalone internet radio, has its own identifiable MAC address.

What do you want to do (just curious) ?
As said by the other posters, you can't and you don't have to.

http://slagheap.net/etherspoof/

never tested in leopard.

Well, I disagree with this: there are legitimate reasons to want to spoof your Ethernet MAC address. One such reason is when your ISP is tied to your ethernet MAC address and you have a hardware failure. Simply spoof the addresse, and you are back online, if only to ask your ISP to change your MAC address (and if you're lucky, it will be done before the end of the next decade).

In Tiger, you could spoof the ethernet address with the ifconfig command:

sudo ifconfig en0 ether <NEW MAC ADDRESS>

I gather this may not work anymore under Leopard. I too would like to find a way.

I'm also looking for a solution to this problem.
The lladr and ether commands do not function on Leopard anymore, and neither does ETHERSPOOF or any other spoof app I've seen.
My theory is that this has to do with the new way Leopard handles network traffic (for example, Little Snitch had to be rewritten).
Anyone who can come up with a solution gets major kudos from me!!!

EDIT: I just found MacDaddyX and it works great for AirPort in Leopard, but doesn't (yet) have support for wired networking. Does anyone have any suggestions or solutions?

I've found that http://spoofmac.com works great in Leopard... for spoofing the AirPort MAC address. Not so much for the ethernet. It seems that something changed in Leopard and I haven't seen any information about spoofing wired MAC addresses and success under Leopard.

(A legitimate reason to spoof a MAC address: I'm trying to get two ports in my apartment swapped from the student subnet to the faculty subnet. The net admin has no idea which cables are involved and wants to trace MAC addresses. I've got a couple of routers plugged into the ports... but no way of getting the routers to go through the web forms to register with our student ResNet and therefore no way to get the routers (and their MAC addresses) out of their ResNet jail, and make them traceable so I can get these ports swapped. So... I'm trying to spoof their MAC addresses on a machine that can go through the web forms to get those MAC addresses out of jail. Unclear if spoofing the MAC addresses on the wireless will suffice. Ay yi yi.)

I just bought a new macbook and this inability to change mac address is killing me! Basically, I've already signed up a contract with an ISP and it somehow remembers my old laptop (windows) mac adddress. Now, when I try to connect my new macbook...i couldn't get access to the internet and the ISP wanted me to resubscribe in order to use the new macbook...

I'm using wired cable connection btw....so I really hope there's a way to clone mac address for the ethernet card using Leopard.

My university library used to allow postgraduate students to use their laptops in the postgraduate research area. Due to budget constraints they no longer do so (it costs time and money for someone to allow the MAC address of your laptop on the network). With Tiger, it was no problem to change the MAC Address of my MBP to the MAC address of the desktop in the workstation I would sit at. Now with Leopard, this doesn't seem to be possible anymore. One workaround I've been using is to use Parallels to connect to the internet through Windows. You can specify the MAC address of the virtual network connection, thus allowing the Windows environment to connect to the network. I wonder if this opens up a possible solution to allow access to the network in the Leopard environment. Can a network connection in Leopard be bridged (is that the right term?) to the virtual connection in Parallels? Or can a piece of software be written for Leopard to create a virtual connection to the internet in much the same way Parallels is able to do it? Just some thoughts and suggestions...

I desperately need that it for wired. USB wifis.

Please apple!!

I need to open a VM, change my mac and connect in linux... share the connection with osx.. lame..