Here's a transcript of a statement to the Joint Economic Committe on the flat tax. It's old- 1995, so the tax rates on the wealthiest are lower now than they were then, but the gist of the argument still holds:
http://www.ctj.org/html/tjmjec.htm
The most interesting thing about the flat tax is that it says interest would not be taxed. Which means those that live off of investments (mostly the super-rich) would pay no income tax, while those of us who work 9-5 would pay tax. Isn't that interesting?