As your question is tagged for both 3.5 and Pathfinder I'll answer for both.
For 3.5 check out the Savage Species splat-book, as Brian noted. It gives a level by level breakdown over the course of 6 levels for how to turn a PC into a Werewolf, though I believe there are some other Lycanthropes listed as well. While this isn't the Savage Species breakdown I was referencing, WOTC released a "Savage Progressions" series on their site breaking down monster races into playable classes. It is worth looking into as you can invest as much or as little as you want into it if you just want the flavor.
For Pathfinder, with DM approval, you could always take the CR+1 Lycanthrope template listed on the Pathfinder SRD (and in the back of the Bestiary.) Essentially it'd be a 2 level multi-class dip but you'd get the flavor you are looking for without wasting levels and still remain an effective Druid. The template itself is for both natural and afflicted Lycanthropes with varying levels of power for each type. Here is the Pathfinder Werewolf in all of its glory if that is the route you are wanting to go, just to give you a better idea of what your Druid would be capable of.
Personally, I have gone both routes at one point or the other. The Savage Species breakdowns are nice and effective but at the cost of a significant level investment. It can feel like your uber-powerful character is weaker than your regular party members at times. I would just go the template route, personally. The level investment is less significant and you still get the flavor you want out of it. Before you decide on either though, I'd talk with your DM just to run it by him as he might have a preference either way.