Thought I would pass this along. I have read several threads about how to program buttons on new key. Most describe the proc that involves holding down unlock and pressing lock 3 times.
I just bought an 04 MC, prod date is 11/03. I ordered new key from dealer (car only came with 1 master key). They shipped it snailmail. Could not get the key programmed no matter what I tried. Even tried what manual said..."press any button 4 times ".
Called dealer, turns out they have to program key. Took 2+ hour drive to them this morning. Took 30 minutes, all is well.
Not sure if this applies to all <7/04 prod dates. But mine is 11/03.
Hope this helps someone else.

 

Yes, it does apply to all earlier prod. dates. You can tell by the key. If it is the really round key in the button surface area, you need it programmed by the dealer. If it is the flatter button key(no rubbery grip, more plastic key), then you can do it just with the car and button press sequence.

Chad