I dunno why you're wasting your time with that controller, it's not as beefy as the original one. However I have used it in windows 7 64bit with no issues whatsoever, this is just a Dell computer, nothing fancy about it.
Are you using command line MAME? I suggest MAME GUI, solely 'cause it's more on par with working with anything hardware related that works with windows. Also, there's the possibility that your MAME isn't "saving" the settings for accepting controller inputs, remember that MAME prioritizes keyboard inputs over any other peripherals. Take a look at the dialogue, you can open it with wordpad, notepad, any text tool, there under setting you'll see the controller input section, make sure it's got the right value, as in yes or no.
As a last resort you could always try JoytoKey if your computer does recognize the NGX controller under windows. Hope that helps.