I just got Win 8 on my new laptop, decided to give it a whiz.
There is a way to have two windows side by side, but it's more 1/3 and 2/3, and the 1/3 portion is more like a 'hold' screen rather than an active/what's happening in that screen.
Since beginning to use Win 8 three weeks ago I have not yet once used the start screen. I even got gung ho about the Windows 8 app store, but the image that was posted above could be used for the exact same reason. Ain't nothing in there.
I had it on my laptop before it died. You can run it in desktop mode, bottom left corner by default. Which is looks /behaves like win7. This is actually where I spent most of my time, because that is where Virtual Studio ran.
As Scarlet mentioned, in the Modern (Metro) environment there are three states, fullscreen, snapped (1/3 screen) and filled ( the other 2/3 screen). This was the case when I did a couple of ms dev and ux workshops late last year.
My experience was that the Modern (Metro) interface was generally for information consumption, and the trad desktop was for work.