Barack Obama (web|news|bio) prepared Thursday to accept the Democratic presidential nomination during a massive rally in front of a crowd of 75,000 people at Invesco Field at Mile High.

Millions more will watch from home as the first-ever black major-party presidential candidate makes the case for his candidacy to the nation on the 45th anniversary of Martin Luther King Jr.'s 'I Have a Dream' speech.

Obama's campaign said the speech will be a direct conversation with voters.

"Senator Obama's speech tonight will be as he himself has characterized it, more workmanlike, a very direct conversation with the American people about the choice we face in this election. About the risk of staying on the same path we're on, the risk of just more of the same versus the change we need," Obama spokeswoman Anita Dunn said in a conference call with reporters.

Obama, who first gained national prominence just four years ago in a speech to the 2004 Democratic Convention as a little-known Illinois state senator, was also expected to draw contrasts with rival John McCain (web|news|bio) and try to dispel any remaining concerns Americans might have about his capability to govern.

"He needs to take a few cues from Bill Clinton, and let average Americans know he understands what they're going through," said Politico's Daniel Reilly.

Workers put the finishing touches on the stage Thursday, which has been criticized by Republicans.

The stage features a row of Greek-style columns in the background.

"This Roman-like facade, a facade with Roman columns, is a perfect metaphor or icon for the point that it's an interesting production, but behind it there's not much there," Minnesota Republican Gov. Tim Pawlenty told ABC.

In a surprise appearance at the convention Wednesday night, Obama told Democrats why his campaign moved the acceptance speech from the Pepsi Center.

"And so we want to open up this convention to make sure that everybody who wants to come can join in the party and join in the effort to take America back," he said Wednesday.

Among those speaking before Obama include Virginia Gov. Tim Kaine, who was mentioned as a possible running mate for Obama.