The Greens have an interesting idea there about abolishing the Senate. They want to form a single congressional body where representation is proportional to population. I don't think the people of this country would ultimately want that, but I can understand the motives behind proposing it. The Green party is too idealistic for its own good sometimes.
As for Nader's differences with the Greens, I think he's more independent than any of the other candidates. First of all, the Green Party actually sought out Nader - they wanted him to run on their ticket. He didn't ask to be their candidate.
Its all over their web site that "this is not Nader's platform", and for good reason. He is an independent who is running as a Green Party candidate because he agrees with them in a lot of areas, and because they have grassroots resources that he needs. His campaign is not swimming in money the way Gore's and Bush's are, so allying himself with the Greens is important to his success.