just google "replace bottom of pinball cabinet". lots of results with pictures. I know people who have done it (I think newtoit did one, he did a short write up on pinside), but I have not tackled one of those myself. here's one how-to...good luck.
http://www.pinrepair.com/restore/index1.htm#bottom
THANKS!!! That looks like it is easy enough to do.. I am a handyman and love working with wood!!