Actually I believe that Dean was born a Catholic.
But raised Joe Piscapo-lian, according to this article in the American prospect:
http://www.prospect.org/print/V14/10/franke-ruta-g.html Starting 6 paragraphs from the end of the article:
"Dean's own conversion to Congregationalism was a more mundane political affair. He'd been christened as a Catholic and was raised Episcopalian. But he converted to the local Vermont religion as a consequence of his battle to make over the shoreline. "I had a big fight with a local Episcopal church about 25 years ago over the bike path," he told This Week with George Stephanopoulos in September. "We were trying to get the bike path built. They had control of a mile and a half of railroad bed, and they decided they would pursue a property-rights suit to refuse to allow the bike path to be developed." Dean eventually talked church leaders out of the lawsuit, recalls Sharp, but other railroad neighbors refused to budge and litigated the case all the way to U.S. Supreme Court.
The effort to restore the Lake Champlain shoreline was a turning point for Dean in his transformation from New Yorker to Vermonter: At the same moment, he both adopted the local faith and became involved in local politics. To this day, Dean remains devoted to the idea of local freedoms, local governing solutions and local control. He supports the assault-weapons ban, but other than that, prefers each state to draft its own gun-control laws -- a position that's earned him an "A" rating from the National Rifle Association. He signed the court-ordered civil-unions law in Vermont -- indeed, one lesbian couple in the suit that led to the law belong to the same Congregationalist church as Dean -- but does not favor any federal law on marriage. He's ferociously opposed to unfunded mandates that make impositions on state governments, such as the No Child Left Behind Act. "
A CBS source about his cafeteria religious journey:
http://216.239.37.104/search?q=cache:TJD5uMVzbWAJ:www.cbsnews.com/stories/2003/10/21/60II/main579140.shtml+congregationalist+episcopalian+catholic+%22howard+dean%22&hl=en&ie=UTF-8