Hillary Clinton is preparing for her last hurrah of the 2008 election with a prime-time address to the Democratic National Convention Tuesday night.

The speech, likely to eclipse that of keynote speaker Mark Warner, former governor of Virginia and current U.S. Senate candidate, is her final opportunity to soften tensions between her supporters and Barack Obama before the Illinois senator is formally nominated Wednesday.

Amid lingering hurt feelings, Clinton is expected to release her delegates Wednesday afternoon. She and Obama's supporters earlier worked to sign on the requisite 300 signatures needed to put her name into nomination, with the intent of acknowledging her historic bid without disrupting the convention roll call. It has been discussed that Clinton would cut the roll call short and call on her delegates to unanimously back Obama.

However, FOX News has learned that negotiations under way to work out how the roll call would proceed have been taken over by the Obama camp, which is now informing Clinton's supporters on how the Wednesday vote will transpire.

Despite the behind-the-scenes hand-wringing, party chairman Howard Dean said convention-goers are in lockstep behind Obama. "There is not a unity problem. If anyone doubts that, wait till you see Hillary Clinton's speech," he said.

Asked if she was excited while she and daughter Chelsea had an afternoon walk-through at the Pepsi Center, Clinton smiled and said: "You bet!"

She came out in a beige pantsuit, as onlookers swarmed around to see her and snap photos.

Clinton supporters fought the storyline that her delegation is divided.

"No one likes to lose. We had a long, tough campaign fight," said Terry McAuliffe, Clinton's former campaign chairman. But he said most her supporters have come over to Obama's side.

"There's gonna be some holdout. I think tonight though for most people ... she's going to give the reasons why they have to support Senator Obama," he said. "And we're all going to be together -- one unified party."

Clinton's primary campaign team has been a constant presence so far at the convention, and several supporters have praised her for her efforts.

Howard Wolfson, former Clinton communications director and now a FOX News contributor, said Clinton's speech has been written with Obama in mind, and his staff should be pleased with it.

"We do know that a lot of her supporters are looking to her, are going to tune in tonight, do want to know what she says about Barack Obama, and she is going to give a full-throated enthusiastic endorsement, urge her delegates, her supporters, her voters, 18 million of them, to get behind him to work for him to get him elected president. She is going to say if you believe what I believe if you fought for what I fought for it is now time to back Barack Obama," Wolfson said.

But even as Clinton tries to put to rest claims of disunity within the Democratic Party, Republican John McCain aired a new television ad -- which started running at 5 a.m. ET Tuesday, or notably 3 a.m. in Denver -- that plays off Clinton's primary campaign spot featuring sleeping children and a 3 a.m. phone call portending a crisis.

In the new ad, Clinton is quoted from the primary season saying: "I know Sen. McCain has a lifetime of experience that he will bring to the White House. And, Sen. Obama has a speech he gave in 2002."

A narrator adds: "Hillary's right. John McCain for president."

Clinton has already denounced such tactics from McCain, telling supporters after similar efforts to use her words against Obama, "I'm Hillary Clinton and I do not approve that message."

It's a turnabout for Clinton, who once seemed to have the nomination in her grasp and now is being called on to defend and support the person who wrested it from her. She is effectively playing middlewoman Tuesday night -- passing a torch from her husband, the 42nd president, to Obama, who wants to succeed him as the next Democratic president.

Ceding the 2008 contest to Obama does not necessarily mark the end of Clinton's presidential ambitions.

At 60, she could easily chase her dream in a future White House contest, activating the fierce loyalists and the women who dreamed of a female president -- and perhaps calling in an IOU from a future President Obama.

FOX News' Carl Cameron and The Associated Press contributed to this report.