That poll question seems both vague and oddly slanted in that it calls the generic plan to roll back Bush's tax cuts for the wealthy Hillary's plan when all the Democratic candidates have offered this same proposal:
Although they have yet to release detailed proposals or to talk about the issue in any depth on the campaign trail, Senators Hillary Rodham Clinton and Barack Obama, and former Senator John Edwards, said through aides that they were backing variants of the same approach, which would result in higher taxes on income, capital gains and stock dividends for upper-income people. All of them, as well Senators Christopher J. Dodd and Joseph R. Biden Jr. and Gov. Bill Richardson, have made clear that they would support keeping in place the tax cuts that have benefited the vast majority of people, roughly speaking households with income less than $200,000 or so. In that way, the Democratic stance would ensure that a substantial portion of one of Mr. Bush’s signature policies would outlast his presidency, even if his party loses the White House.
http://www.nytimes.com/2007/04/21/us/politics/21tax.html