The wordcasting system was pretty barebones when it was released and has received absolutely no support in the years since. The only class lists that were given enough words to actually be playable are the Wizard/Sorcerer and Cleric/Oracle. Everything else is just so barren that it basically doesn't function - and the druid is included. I would only recommend wordcasting for Sorcerers and Oracles.
I've tried playing word casting prepared spell casters (Druid was one, as I love Druids) and I can say that you are better off using words of power with spontaneous spell casters, as Dasrak said. Being able to mix and match your spell targets/effects/saving throws is an incredible boon for spontaneous casters, gaining a different type of versatility than what you lose by using normal casting.
In short, don't do it with a Druid.