Jimmy Fallon Jimmy Fallon

To prep for his March 2 takeover of NBC's Late Night, Jimmy Fallon is turning to the only people who truly understand the challenge ahead: other talk show hosts.

"I just recently ran into Rosie O'Donnell at a Paul Simon concert and she said, 'Who's doing your test shows?' ... She said, 'I'll do one.' I thought that was so nice of her. So she's gonna come on next Thursday and do a show."

Fallon's first real guests will be Robert De Niro and Van Morrison. He's gotten good wishes from Jimmy Kimmel — with whom he'll compete for ratings for part of his broadcast — Ellen DeGeneres and Garry Shandling.

He also got some wisdom from the late Tonight Show host Johnny Carson, by way of his Late Night predecessor Conan O'Brien and Stephen Colbert.

"Colbert told me, 'I'll tell you something that Conan gave to me, that Carson gave to Conan. And that was, with the show, you'll use everything you know,'" Fallon said in a conference call with reporters Thursday.

O'Brien has also offered his own advice.

TVGuide.com asked Fallon if there was any advice he wishes he could have given himself when he first got the job.

"Calm down, it's all gonna happen," he said. "I remember at one point I'm like, 'Oh my God' — it was like eight months away — 'I can't wait for it... it's so far away.' And now it's like, it's here. It's here and I'm ready to go. The nerves are out of me now.

"I'm ready to go on tomorrow night. If NBC needs me, I'm ready."

But the network doesn't need him just yet: O'Brien still has to say goodbye to Late Night on Friday.

What suggestions do you have for Fallon? Will you watch his show?