shamatha meditation brings calmness and discipline to the mind, vipassana means insight, insight into reality as it is, this meditation is done after the mind is calm and disciplined. Jhanas are another kind of meditation and they take you through all the levels of the mind , refining concentration and eventually you will have to let go of these subtle mind states as well.. Each Jhana becomes more subtle, more subtle until there is nothing left to grasp...

I like Liegh's site, he speaks about Jhanas in a way that is very understandable to me.

http://www.leighb.com/jhanas.htm