If there is a “new” (spoofed) MAC for the adapter, it is shown in box number (3), and if it has a known OID the corrisponding manufacturer is show in box (4).
You can go back to your original MAC address by pressing Remove at this moment.
You can spoof the address by typing the new one into the box (3), or selecting a manufacturer from box (4). This creates a new MAC with the chosen OID and “123456” as device ID. Of course, you can change the device ID as you like.
Now just press Change and check the log for any errors. After disabling/enabling the adapter, your new MAC is in place.
That’s all!
Also, if you start typing an OID into the box (3), there is an automatic lookup function that tells you what manufacturer you are referring to. Starting from version 1.91d Mac Makeup look for an installation of Wireshark: if you have it, the program will use tha OID database that ships with that tool. Authors of Wireshark made a great job with the sniffer and continuously update their manufacturers signature database. Also if you don't know Wireshark you're missing a very good network analyzer.
New from version 1.23d is the ability to filter out virtual interfaces. The filter is on by default, but you can disable it by clearing the check (5). Virtual interfaces are referread as the ones not being physical. From version 1.83d the filtering engine was revised to be more accurate and support different types of cards. Also the bus to which they are attached to is displayed.
If you check MAC History (8) the program looks for a file named mmkup.ini. This file contains the history of MAC addresses used on a per interface basis: this way you can use the combo box (3) to cycle through spoofed addresses. The file is located into the same directory of the main executable.
If you need to save the log window or clear it, just right-click on (2) and select the proper action from the popup menu.

Auto nic off/on (9) is new from version 1.83d and lets you disable and then reenable the network interface when you spoof its address. This way the change is immediate, no more need to open network connections applet or use external tools. The 'Cycle interface now' just disables/reenables the interface when you press it.

If you press (10) you have this  menu that lets you generate a completely random mac address, a random device ID (mantaining the OID), or a new OID (mantaining device ID) taken from the database or autogenerated.

The log window now contains extra infos for any interface selected. Not all of these info are available all the times, dependig on the system settings, version and nic driver interfaces (it is fully functional with Windows XP SP2 and Broadcom 57x drivers for example).
These infos contain the real MAC address of your network interface (PermanentAddress), speed, IPs and so on.
Since it requires some seconds to load these infos, by default the Extra info checkbox (7) is disabled since it contains beta code and needs further testing.

IP Extra features

IP Extra features are available by clicking "IP estra features" (6). These options let you enable, disable or configure several aspect of Windows NT IP networking.
Figure below shows the options you can set:

Options can have three colors: red, black and blue.
Blue options are the ones not defined on your computer, meaning that Microsoft's default values will be used. The great part of IP Extra features are not defined by default, and this may vary depending on the software you've installed.
Black options are set, and their values will be used as shown.
Red options are the ones you are going to undefine (remove). 
You can change the status of each parameter by right-clicking on the description and cycling though colors. Only defined (black) values are set pressing the "Apply" button. Undefined (blue) parameters are ignored. Undefined values are shown with their Microsoft default, so setting them without modifying the value should lead to no changes.
Please note there's a difference between undefined and defined but unchecked (for example).

The first thing you should do before experimenting, is taking a backup snapshot of your current configuration by pressing the "backup current settings button". This will ask you for a location to store a .reg (windows registry) file; double click on it at any time to revert to the starting situation.

Here is a very brief discussion about these parameters. Refer to Microsoft Technet documentation for any doubt. Please note that some of these directly impact your station's security.

The command line mode

Mac Makeup has a command line mode since version 1.83d. This lets you script maniacs to include it into batches and set the new MAC addresses without intervention. You can disable/enable your interfaces with the devcon tool, you can find for free on Microsoft web site.

Command line usage:
macmakeup.exe <count | <set | SET> <interface> <new_mac | random> | clear <interface> [quiet]

enum: get a list of all the interfaces present, even virtual ones

set <interface> <mac>: sets <mac> on interface number <interface>
Just like: macmakeup.exe set 4 010203040506

If you use 'random' (without quotes) Mac Makeup will generate a random mac address for you.
Example: macmakeup.exe set 4 random
If you use 'SET' (with capital letters) the interface will be disabled and reenabled to make the mac change effective.

clear <interface>: reset back to original mac address interface number <interface>
Example: macmakeup clear 4

quiet: optional parameter that sets the output mode to quiet, so that you 
have no kind of output.

If you don't use "quiet", the output of the program goes to a console. If the operations complete ok, then the console is closed. If there is some kind of error, the console is kept open and you're asked for confirmation before closing.

I have some questions…

Look at these FAQs.

Usage License

Don't worry, the program is always FREE software, just a couple of details...

By using this application, you agree to the terms below:
- You are granted to use this program for FREE, as it is FREE software
- You are allowed to use this program on one or more machines at a time
- You are allowed to distribute this program as long as you do it without profit and without modifications to this license (See note at the end)
- You may not modify or reverse engineer this program
- You may redistribute this program included as a support tool for your programs, as long you notify me by mail, get a positive reply and insert a note into tour software indicating the presence of Mac Makeup(*)
- The author has no obligation to provide assistance, defect correction or any kind of maintenance for this program
- Your are allowed to use it in any government environment. In this case an email notification to the author is appreciated

You CANNOT use this program if
- you intend to break into other people's networks
- you use it to access information you are not entitled to view
- you are a terrorist of any kind
- you don't know what you're doing, as you can disrupt network operations

If you don't agree, you MUST delete all the copies of this program.

(*) Really there is no reason to get a negative reply, only want to get stats and usage examples

BartPE Plugin

You can use Mac Makeup from 1.97d as a BartPE Plugin.