Ignition coil as nst substitute?

I would like to make a small coil as a first attempt. I've read with
interest the recent posts on 
using an ignition coil as the actual secondary, and it seems they can take
a lot of abuse. I have 
also seen a PSU made with 2 ignition coils, a capacitor and a light dimmer
on a page called 
Greg's Garage (I can't remember the URL off hand), the author of the page
mentions that he used a 
similar psu to power a small coil. 

Does anyone have any experience of putting mains through ignition coils?
What is a safe number of 
watts to put through a coil (or 2) at 240vac? What sort of output voltage
will I get? I am not 
aiming for big sparks, I just want to start out with something small! Also,
could anyone 
recommend a program that will let me design a coil based on the psu? I've
been using Tesla 
Designer by Walt Noon, but I'de like to have a second opinion.