I did it a few days ago having never done it before, but, really, putting back together is just the opposite of taking apart - the difficult bit is the ribbon cable; remeber to keep a twist in it and put it back under the foam behind the screen. Also, make sure you get the buttons in correctly - I had to take it apart because the letters were facing the wrong way and I (bizarrely) had to press the start button every time my M3 Real wanted to read from the microSD. Don't ask me why.
UPDATE:
I just found these websites I used:
http://forums.maxconsole.net/showthread.php?t=81938
http://site.powergamingparts.com/RepairNDS.html