Tesla Coil CAD is a great program written by Richard Chapman.
This program allows you to enter in parameters about your transformer, primary and secondary, and will give you info on how many turns to make your primary, what capacitance is needed for the primary circuit and much more.

You can learn more and/or download this great program by clicking the following link: http://www.geocities.com/~richards_place/tesladownload.htm
Tesla Coil CAD,Copyright 1996-2001, Richard Chapman, all rights reserved.
Click here to see and download TCCAD designs of my coils.