I use kettlebells a lot for my own workouts and when I train clients. Quite honestly, I think they are a current workout fad. They are great, but there's really nothing magic about what you can do with them. You can pretty much do the dame thing with dumbbells. They are expensive and don't come in as many different graduated weights.
If you belong to a gym with kettlebells and a knowledgeable trainer, that would be a good place to start. But I wouldn't go buy a set for home workouts.
There is an article on www.stumptuous.com about them, there's also a link to the kettlestack where you can change the plates like you can on dumbbells.
But like Mel said, if you can do it with kettlebells, you can do it with dumbbells! There are also some examples of doing kettlebell workouts with dumbbells on stumptuous!