How is the nominee decided?

I'll admit, my knowledge of the party nominating process isn't as great as many others here.

But let me get this straight, is it based on the total number of delegates each democrat has? Is it like electoral votes, where the candidate must win a certain number to win?

And how are the delegates chosen? What is the difference between a primary and a caucus? As I understand caucuses aren't as open and don't draw as much turnout...I may be wrong though.

Also what do people here think about open primaries? I know McCain won Mi and NH because of open primaries in Mi (not sure about NH though, but I think they're open). Do you think it's good to allow cross over votes determining the party's nominee or do you view it as outside interference?

I tried googling this, but I couldn't a good website that explains the process clearly. Maybe someone could give me a good link.

Each candidate is seeking delegates that are obliged to cast
ballots for them at the convention. primaries and caucuses are
held to determine this.

A primary is a vote of the electorate to choose the best
candidate from the list. The delegates are cast according
to the total vote. A caucus is a meeting of people who are
wooed by candidates and vote in small groups to support a
candidate.

At the election they are bound to a certain number of
election cycles before they become free to select the
candidate they want. Perhaps three or four ballotings
are held with you pledging your bound candidate before
you are freed to make a different selection.

In the past, open primaries never bothered me but now
they do with the lack of ethics and win at any cost
mentality of the bush machine.