From the Jamuary 2004 Vanity Fair profile of Joe Wilson (found here):
In early May , Wilson and Plame attended a conference sponsored by the Senate Democratic Policy Committee, at which Wilson spoke about Iraq; one of the other panelists was the New York Times journalist Nicholas Kristof. Over breakfast the next morning with Kristof and his wife, Wilson told about his trip to Niger and said Kristof could write about it, but not name him. At this point what he wanted, Wilson says, was for the government to correct the record. "I felt that on issues as important to our whole society as sending our sons and daughters to kill and die for our national security we as a society and our government have a responsibility to our people to ensure that the debate is carried out in a way that reflects the solemnity of the decision being taken," he says.I've always thought the Wilson to Kristof to Miller path was a pretty good explanation for how Miller learned about Plame's CIA job.