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Jimmy Fallon, as previously reported, will take over for Conan O’Brien when the red-headed comedian makes his long-planned move into Jay Leno’s seat at The Tonight Show. NBC made the deal official at a press conference today with Fallon and exec producer Lorne Michaels. Further details were in short supply, from Fallon’s contract length and salary (“I keep asking Lorne, and he keeps telling me not to worry about it,” Fallon cracked) to show specifics and the key question of when the transition will take place. “Sometime in ’09,” hedged Michaels, who’ll produce both O’Brien’s and Fallon’s shows. “Probably the first six months. Maybe the second six.”

Why so cagey about the exact date? The net’s still negotiating to keep Leno in the family and avoid having late-night’s most-successful host be most-successful at another net. Co-chairman of NBC Entertainment Ben Silverman told that doing so could involve primetime, cable, syndication, or some combination thereof. “We love Jay and want to keep him around,” Silverman reiterated.

Fallon, meanwhile, promised to make his “the best show for everyone to fall asleep during” and said he’s been doing standup lately to get into practice. “We’re not going to reinvent the wheel,” he said of the show’s format. “But when Conan took over for Letterman, he wasn’t Letterman. Oh, and all the furniture will be suspended six feet in the air.”