Read all of these articles on this page and you'll have a better understanding of how a turbo works.
http://www.howstuffworks.com/turbo.htm
I think that you will be best off with the greddy kit as well but I've also heard that the F-MAX kits are pretty good, but they seem really expensive to me.
http://www.f-max.com/
http://www.greddy.com/
Good Luck!
