Submitted: 4 weeks ago - U.S. Sen. Hillary Clinton (D-N.Y.) will campaign at a Henderson high school Friday on behalf of her former rival, U.S. Sen. Barack Obama (D-Ill.), the Obama camp said Wednesday. Clinton is scheduled to appear at a campaign rally beginning at 11 a.m. at Green Valley High School. The Obama campaign is using the event to jump start a voter registration drive over the weekend. Obama, the presumptive…