My stealth mode works, but I do have the same problem.

Whenever I press the stealth mode button, it enables stealth mode, but presses "W" at the same time?

I dont understand why it does this, but its not really that aggrevating. I would like it fixed though.

Yeah, it is not that bad

but I think they should really solve this problem cuz they are "Aliens", 

and the problem is somewhat stupid

Anyway

thanks for your help, man

What's the Stealth button for and where is it?
Maybe the M17x doesn't have it???

The M17x does have it.  Its on your soft buttons on the top right above the keyboard.  It turns off your descrete video card and uses the onboard graphics card(lower performance), so its mainly for when you are using your battery and do not want to drain it.  It looks like your speedometer(the button looks like it) in your car, and yes it does work, and no I have not seen it call it the W button when using.

Stealth mode turns off the high performance of the graphics card (for me dual 5870's) and uses the graphics card that is built into the mother board.  This is generally used when you are using your battery to get better life out of it.

What is it supposed to do?
I could find out in the manual but I left that in the original box which is packed away in the loft.

So you would get the same kind of resolution and colours that you have in safe mode, right?

No its better then safe mode.  Safe mode doesn't load your video drivers, so that is why safe mode looks so horrible.  I can still run a game in stealth mode, but I need to turn everything way down.  Its just a way to get graphics without your battery being eaten by the high performance graphic card.

So, if it only works in AC mode, what is the point of it?

Stealth Mode only works when you are plugged into the AC Adapter. When running on battery power, stealth mode is not available, because the computer is already in a low power consumption state.