Imagine shaping your own presidential showdown, using candidates and their answers like building blocks that shatter the standard conventions of a televised political debate.

Yahoo! and the blog HuffingtonPost.com and the Web magazine Slate.com this week will let viewers assemble their own presidential confrontations. They can stack one candidate against another, or line them all up by single issue.

PBS' Charlie Rose will be the moderator and interviewer who will elicit the answer blocks in a series of interviews Wednesday with the eight Democratic presidential candidates. Rose will quiz each candidate separately, by satellite from New York, on topics selected by a vote of Yahoo! users.

Once posted on the three Web sites on Thursday, viewers will be able to edit to taste. Joe Biden vs. Barack Obama on the war in Iraq. Hillary Rodham Clinton on health care, education and the war. All eight on a "wild card" question reserved for each one. And more.

Call it Web 2.0 politics. Or, call it what its organizers do — a "mashup."

The experiment is the latest offspring of the marriage of politics and the Internet. Presidential candidates have ventured onto online social networking sites such as Facebook and MySpace. They've established elaborate interactive Web pages to spread their message and raise money. They've learned to advertise based on keyword searches. They've participated in online town halls sponsored by the liberal MoveOn.org. And they've lived, and suffered, by the power of YouTube.

"The point is putting power in the hands of the audience and letting them navigate it," said Scott Moore, Yahoo's senior vice president of news and information.

The idea, said Huffington Post's Arianna Huffington, was to reach an audience made up particularly of young people who typically do not get their information from traditional media sources.

"If we're going to increase their political participation we have to meet them where they are," she said. "That was the idea of the mashup — that is, to empower users to create their own tailored candidate forum experience....They may not sit spellbound for an hour and a half."

Rose will ask the candidates questions on four categories: the war, health care, education and one undisclosed candidate-specific subject. As the interviewer, Rose will be allowed to follow up and to slightly alter the questions to fit the circumstance.

The eight interviews, if watched in one chronological sitting, would last about two hours. But that's so old media.

"A big part of this for us is to try to innovate and do something that hasn't been done before," Moore said.

For the candidates, the format permits them to reach an audience without major scheduling upheavals. They'll connect with Rose from wherever they happen to be campaigning. Several of the candidates who are members of Congress will participate from Washington.

So far, only the Democrats have agreed to be part of such a debate. Moore, Huffington and Slate's Jacob Weisberg want to have a similar exchange with Republicans. Once the parties have their nominees, Moore said he'd like to stage an event that would also allow the candidates to interact with each other.

Others are testing the Internet, too. MySpace and MTV plan to hold real-time online conversations between the candidates and young voters, who will be able to instant-message, e-mail or phone text their questions. The exchanges will be Webcast live on MTV.com and MySpaceTV.com starting later this month through December.

"If you think back to the 1960 (presidential) campaign, that was the first time that television had a material impact on the election, on who won," Moore said, referring to the televised debates between John F. Kennedy and Richard Nixon. "I believe that 2008 will be the first time that the Internet will have a material impact on who wins the election."