It's not completely clear to me whether folks here may be talking about two different things:
Google Now is, to my understanding, the feature that not only provides a search option but also automatically shows cards that provide you with additional information, such as local weather, your appointments for the day, stock market information, your commute time, etc., according to the options you select.
Google Now. It can be accessed by long pressing the menu key, or pressing "Google" in the Google widget (the one that is on the home screen on the GN2 out of the box). Unless there is a setting to avoid it that I can't find, the keyboard (or writing tablet - whichever you've selected) always pops up with Google Now, and the keyboard can be closed by pressing the back key, which does
not start Google Voice Search, and which leaves the rest of the Google Now cards in view.
Google Voice Search, which it appears the opening post was asking about, can be directly accessed by pressing the microphone icon at the right of the Google widget on the home screen. That will bring up the Google voice search function, without the keyboard and without the rest of the Google Now functions, just pure search.
Google Voice Search. Or, from Google Now, either say "Google" or press the microphone icon at the right side of the search field at the top of the page, to start Google Voice Search.