Stop ! - you may not need to take the keyboard out to fix your broken letters - you can pop-off the key caps - clean up with an old toothbrush and pop the key caps back on again - tweezers help.
Check out this link before dismantling your machine...
http://www.laptoprepair101.com/laptop/2007/03/20/key-fell-off-keyboard/
Good luck...
Peccavi
April 2010