Wikipedia has a great explanation about delegates and how many it takes to win, etc. I only checked out the Dems, but they have it for both parties.
Each Dem representative, senator and governor are automatically delegates in addition to others that are pointed out on Wiki. These delegates can "endorse" a candidate so right now Hillary has 154, Obama has 50, Edwards has 33, Richardson has 9 and Kucinich has 1 (likely his own).
Each state is allocated a number of delegates based on population, etc. Some of the delegates are pledged and after the caucus or primary, the pledged delegates are allocated to each candidate based on the percentage of the vote that they get.
In Iowa, there were 45 Pledged delegates: Obama got 16, Hillary 15 and Edwards 14 (don't ask me why Edwards didn't get the 15, but he didn't).
Pledged delegates do not have to vote for their candidate at the convention, but can be removed by the candidate if s/he senses that there will be problems, so the pledged number is pretty much what the candidate goes into the convention with.
To get the nomination on the first ballot (August 25-28, Denver), s/he will need 2025 delegates.
If no one has 2025, then after the first ballot, the delegates can vote for whomever they like.
So, technically, Obama can "win" every state and still not have enough delegates to get the nomination.
Also, in addition to Michigan not being allowed any delegates, neither is Florida.