A google for "word search game" turns up a bunch of sites that offer this sort of diversion on the web -- nice to scan for ideas on how to structure an application, but I don't know if you'll find any source code or implementation details that way.

I'm guessing the tricky part is figuring out how to assign the letters to the grid positions so that all the words on a given list are attested just once each. If you can get your head around an algorithm for that, the rest should be easy. The use of a basic canvas widget to draw the grid is attractive, because it would be easy to overlay any other kind of graphic to mark words in the grid when they're found.