1) Create or pick a folder you want to hide it away in.
2) Select another app you want to folder (you can just take one out of a folder to use for this) and move it into the folder.
3) As you you "drop" the App into the folder, immediately drag Newsstand in after it. It should folder.
Just note that if you want to access Newsstand you'll need to take it back out of the folder as it will crash Springboard if you try and access it.
edit: Actually this is quite hard to do on the 4S, sorry guys

. On my iP4 the whole process is very slightly slower you have enough time to drag Newsstand in.