How does it work?
Basically, joints are stabilised by passive structures such as ligaments and cartilage and by active structures - muscles. The muscles can be divided into 2 types:

a) some of the muscles are responsible for moving the joint and

b) some are responsible for keeping the joint stable.

Because the weight of the kettlebell moves when you exercise with it the stabilising muscles have to work as hard if not harder than the movers. Therefore you are training the stabilisers and the movers at the same time. To have an idea of this put one hand on a football and the other hand on another football and do a press up! In the joint (shoulder for example) the stabilisers are trying to stop unwanted movement and the movers are creating desired movement, this gives you controlled coordinated movement. What this also does is take the stress off the passive structures and prevents unwanted stress on the joint.

Where do I get one from and how much?

OK, kettlebell's cost about £70'ish. Jack got his through www.powerseekers.com where they are the cheapest he could find. This may seem like a lot of cash for what is basically a cannonball with a handle but having bought his first one (24kg) back in April last year he watched his strength increase 3 fold! NO LIE!  But you can do anything and everything with it.

Links

Have a look at the links below to learn more about kettlebelling.

www.hard-style.com

www.londonkettlebells.com

www.powerseekers.com

http://kettlebell.tv/video.html

www.youtube.com/watch?v=3NDDES5CEXw

www.youtube.com/watch?v=KglRMrIRvIc

www.russiankettlebells.com