Paszkiewicz's letter shows that his knowledge of the Founding Fathers and the First Amendment comes from crackpot pseudo-historian David Barton. He misrepresents the views of Jefferson, Washington, and Franklin using out-of-context and fabricated quotations, makes the bogus argument that because the words "separation of church and state" aren't in the U.S. Constitution that the concept isn't there either, and generally shows that he doesn't understand the subject matter he teaches.
Kennesaw State University history professor David Parker shows that Paszkiewicz's alleged Jefferson quotation from an April 21, 1803 letter to Benjamin Rush is not found in that letter. (There's something somewhat similar, but Paszkiewicz's version changes the meaning by dishonestly adding and removing words from what Jefferson actually wrote.) Paszkiewicz misrepresents Jefferson's religious views, failing to recognize that Jefferson did not believe in the divinity or miracles of Jesus, and edited the gospels into "Life and Morals of Jesus of Nazareth" (sometimes known as the "Jefferson Bible") by removing all of the miracles.
Ed Brayton at Dispatches from the Culture Wars addresses Paszkiewicz's claims in more detail, showing that he doesn't understand the role of the U.S. judicial system.
Mr. Paszkiewicz, already considered a fool, has spoken and removed all doubt.
(Hat tip to Pharyngula.)
UPDATE (January 15, 2007): I've removed the statement that Ed Brayton has shown that Paszkiewicz used a fabricated Washington quotation, though it appears Washington didn't mean what Paszkiewicz thought he did, and Paszkiewicz didn't quote it correctly. The correct quotation, part of Washington's advice for assimilation, is "You do well to wish to learn our arts and ways of life, and above all, the religion of Jesus Christ. These will make you a greater and happier people than you are. Congress will do every thing they can to assist you in this wise intention." He didn't say he believed it, he said to learn it.
An interesting and lengthy examination of the history of the First Amendment's Establishment Clause can be found in Noah Feldman's "The Intellectual Origins of the Establishment Clause" (PDF) from the May 2002 New York University Law Review (vol. 77, pp. 346-428).