There is a lot more than just that.
1996, he admitted to both the Houston Chronicle and the Dallas Morning News he wrote them.
Most damning is in 1995, he did an interview on CSPAN where he admitted writing them. It is hard to argue with video evidence.
http://citizensagainsthate.wordpress.com/
and check this:
http://graphics.thomsonreuters.com/11/12/Solicitation2.pdf
The folks in Iowa really need to read this stuff before they caucus.