Based on the 2003 IRS tax data, the same year referenced in the article in the first post:
The top 1 percent of taxpayers, ranked by adjusted gross income, paid 34.3 percent of all federal income taxes.
The top 5 percent of taxpayers paid 54.4 percent
The top 10 percent of taxpayers paid 65.8 percent
The top 25 percent of taxpayers paid 83.9 percent.
http://www.taxfoundation.org/news/show/250.html