At this point you can put everything back together again in pretty much reverse order. The summary of steps is as follows.
Place heat sinks back on processors.
Insert circuit board back into case.
Reinsert the fans, ensuring to plug in the fans' power connection.
Insert the RF Module/front circuit board.
Screw in front three black screws.
Attach white plastic covering over power button on RF module board, paying attention to the direction arrows on the piece.
Flip Xbox over and insert all small screws. Start in center with small black screws, work out to small silver screws.
Install white airflow guide.
Connect and install the DVD drive, making sure support holes line up on circuit board and paying care to not break the DVD drive eject button assembly.
Place top on Xbox, flip it over, and insert the long black screws.
Install the DVD drive button assembly.
Place the bottom on the Xbox and snap it in to place.
Next put the grey side pieces back where they belong.
Finally, reattach the front faceplate.
All done... now test! And yes, mine does work with it back together again (and I took it apart about five times in under and hour)!