DENVER -- Barack Obama will try to balance the grandeur of his nomination speech setting Thursday night by delivering what his campaign is calling a "direct conversation" with the American people, before a crowd of more than 70,000 in Denver.

Known for his soaring rhetorical skills, the Democratic presidential nominee intends to offer a "workmanlike" acceptance speech that reflects on the direction of the country as much as the aspirations of candidate.

"Four years ago, I stood before you and told you my story of the brief union between a young man from Kenya and a young woman from Kansas who weren’t well-off or well-known, but shared a belief that in America, their son could achieve whatever he put his mind to," Obama is to say, according to excerpts released by the campaign.

A crowd of thousands of delegates and local supporters was cheering and waving signs and American flags as musicians and speakers warmed up the crowd for Obama at Invesco Field Thursday evening.

Obama's running mate Joe Biden made a surprise appearance shortly before Obama was set to speak.

"When we talked about an open convention, this is what Democrats meant," Biden said.

"It is that promise that has always set this country apart – that through hard work and sacrifice, each of us can pursue our individual dreams but still come together as one American family, to ensure that the next generation can pursue their dreams as well. It is why I stand here tonight. Because for two hundred and thirty two years, at each moment when that promise was in jeopardy, ordinary men and women – students and soldiers, farmers and teachers, nurses and janitors -- found the courage to keep it alive," Obama will say.

Continuing to link John McCain to President Bush, Obama will lash out at the administration's foreign policy while addressing the needs of Americans suffering in an economic downturn.

“We measure the strength of our economy not by the number of billionaires we have or the profits of the Fortune 500, but by whether someone with a good idea can take a risk and start a business, or whether the waitress who lives on tips can take a day off to look after a sick kid without losing her job – an economy that honors the dignity of work," Obama will say. “The fundamentals we use to measure economic strength are whether we are living up to that fundamental promise that has made this country great – a promise that is the only reason I am standing here tonight.”

Obama is also expected to give praise to the last Democratic president, Bill Clinton, a favor returned after Clinton offered a rousing speech praising Obama the night before.

"We Democrats have a very different measure of what constitutes progress in this country. We measure progress by how many people can find a job that pays the mortgage; whether you can put away a little extra money at the end of each month so that you can someday watch your child receive her diploma," Obama is to say. "We measure progress in the 23 million new jobs that were created when Bill Clinton was President – when the average American family saw its income go up $7,500 instead of down $2,000 like it has under George Bush."

The candidate also has the job of defining what the central theme of his campaign -- "Change We Can Believe In" -- means in hard policy proposals. Obama is to say that he will invest $150 billion over the next decade in alternative energies – wind and solar power and biofuels; end U.S. dependence on foreign oil in 10 years, rebuild the military and renew direct diplomacy aimed at ending Iran's nuclear ambitions; eliminate capital gains taxes on small businesses that create high-tech, high-pay jobs and cut taxes for 95 percent of all working families.

“Change means a tax code that doesn’t reward the lobbyists who wrote it, but the American workers and small businesses who deserve it," he will say. “Unlike John McCain, I will stop giving tax breaks to corporations that ship our jobs overseas, and I will start giving them to companies that create good jobs right here in America."

Spectators, reporters and delegates mobbed Invesco Field Thursday afternoon under tight security, with several musical acts and speakers warming up the crowd before Obama arrives. He will mark his achievement as the first black presidential nominee of a major party on the 45th anniversary of Martin Luther King Jr.'s "I Have a Dream" speech.

The backdrop: two sets of Greek-inspired columns and what appears to be the front of a mock-government building, with frosted glass windows. The home of the Denver Broncos has been transformed for the event, with seating encircling the platform where Obama will speak and stretching into the bleachers.

Secret Service agents continued to change up the routes for shuttle buses from the Pepsi Center to the Denver Broncos field less than a mile away as a crowd of people snaked down the road nearly all the way back to the Nuggets center.

"(We're) bearing witness to something ... my whole life, it's just Bushes and Clintons. It's time for a change, and he's someone who represents my generation," said Kristin Wheeler, an Obama volunteer from New Mexico, who waited in the long line with her sister Katie to witness the address.

The affair was set up like a sporting event, with the giant monitors of the stadium showing images of enthusiastic spectators and their banners.

Republicans have ridiculed the stadium set-up as "The Temple of Obama," but Obama advisers say the venue was chosen so members of the public could witness the historic event.

"The fact that we can bring 60,000 ... means that we have a real organizing opportunity," Obama spokesman Bill Burton told FOX News. "Am I concerned? No, I feel great about this opportunity.

"I would only be concerned about the McCain campaign sitting in an empty stadium," he quipped, referring to McCain's plans to announce his running mate in Dayton, Ohio, Friday.

Obama's address comes after Joe Biden stepped in to his role as running mate Wednesday night with a scathing attack on John McCain and the Bush administration.

The apparatus of the Democratic National Convention moved the street to Invesco Field at Mile High for the final day of festivities, operating under the campaign's theme of "Change You Can Believe In." Obama, known for his soaring rhetoric, is expected to use his speech to convey a simple message about how he would help his country as president.

"Senator Obama has a job to do out there tonight," Burton said, "which is to go out there and let the American people know where he comes from, where he wants to take this country and lend some specificity to what exactly his plans are when it comes to tax cuts and health care and responsibly ending the war in Iraq. He's going to talk about all of those things in pretty clear terms."

Howard Wolfson, former Hillary Clinton spokesman and FOX News contributor, said Obama has to "do a mixture of poetry and prose."

"Barack Obama is the best speechmaker in politics today so if there's anyone who can deliver with this much expectation, it's him," he said.

The pageantry of the event continued to earn the nominee more Republican criticism that he is a celebrity without substance.

"It looks like they are getting ready for the emperor to arrive don't you think?" asked Minnesota Gov. Tim Pawlenty, one of a few on McCain's vice presidential short list. "And it feeds into the notion of it's a big production, a lot of entertainment, a lot of hoopla and I think with the Roman columns and the facade it is perfect because the facade is for production purposes but there is not much behind it and that's a perfect metaphor for Barack Obama's readiness to be president of the United States."

The Illinois senator enters the momentous day after receiving two full-throated endorsements from Hillary and Bill Clinton. John Kerry, the 2004 presidential nominee for the Democrats, also renewed his support for Obama on Wednesday night.