Just answered my own question: apparently there is only one openly gay member -- Tammy Baldwin.
http://en.wikipedia.org/wiki/Tammy_BaldwinTammy Suzanne Green Baldwin (born February 11, 1962), American politician, is a Democratic member of the United States House of Representatives since 1999, representing the Second Congressional District of Wisconsin
Born and raised in Madison, Wisconsin, Baldwin graduated from Madison West High School in 1980. She earned a bachelor's degree from Smith College in 1984, and a law degree from the University of Wisconsin Law School in 1989.
Baldwin was first elected to political office in 1986 when she was elected to the Dane County, Wisconsin Board of Supervisors, a position that she held until 1994. She served in the Wisconsin State Assembly from 1993 to 1999 and was elected to the House in 1998.
Baldwin is the first woman elected to Congress from the state of Wisconsin, and is currently serving her fourth term. She was also the first ever openly gay non-incumbent to be elected to the House of Representatives, her election having won the backing of the Gay & Lesbian Victory Fund. While two openly gay men serve in the House of Representatives (Barney Frank and Jim Kolbe), she is the only "out" lesbian. Her partner is Lauren Azar.
On July 26, 2004, she spoke at the 2004 Democratic National Convention in prime time on the issue of health care.