I have the same laptop, I found this artile helpful:
http://www.laptoprepair101.com/laptop/2007/03/20/key-fell-off-keyboard/comment-page-9/
Basically, pop a key off beside it and pay attention to how the white clip is positioned on the empty key space. Align your popped on the same way. Pop the white clip onto the base of the computer keyboard, then take the key and when you push down it should click into place.
Greg
November 2007