This does not mean that he cannot win the election, in order for him to do it we have to look at which states are reliably Democratic:
270 electoral votes needed to win:
Washington
Oregon
California
Hawaii
Minnesota
Wisconsin
Illinois
Michigan
New York
Vermont
Maine
Mass.
Rhode Island
New Jersey
Delaware
Maryland
DC
= 215 votes, 80% of votes needed to win
Crucially Obama would need to win Pennsylvania, but that would only boost him to 236 votes meaning he would need an additional 34 votes to clinch the nomination. Assuming he cannot win Ohio or Florida, I suspect he can win Ohio easier than Florida due to the economic malaise. Obama would have to make the argument to the super-delegates that he can win non-traditional states.
It is within the realm of possibility that Obama could win Colorado, Nevada, and New Mexico would would net him another 19 votes. This would boost his total to 255 votes, these states will probably go to Obama by razor thin margins, so it is a real gamble for the Democratic party to put their cards on that game. Additionally, these states are near Arizona where pro-McCain propaganda will be intense. Also another possible negative for the Democrats is that in this region there is a large latino community, which has not warmed up to Obama.
Thus, Obama will have to probably push the immigration debate hard in order to get those crucial latino votes in the region. This will cause a reaction from McCain which could very well end McCain's chances of getting the latino vote. Thus, it is wise for Obama to push the immigration debate as hard as he can, because McCain will lose either way. Either McCain will lose the Republican base if he panders to the latinos, or visa vera.
Iowa looks like a state that is really trending towards Obama as well, so that would net him another 7 votes, giving him a total of 262 votes, leaving eight votes left. This means that Obama would have to make a make or break for either Virginia, North Carolina, or combine New Hampshire and West Virginia, or even South Carolina. I personally believe that the most realistic scenario will have Indiana shift to the Democratic column, if Indiana does so then the election is over.