vikings/nfl

As recently as two weeks ago, quarterback Tarvaris Jackson was running the Vikings scout team. His receivers were practice-squad players, his plays were designed to emulate opposing teams and his long-term focus was to prepare for a debut that figured to come in 2007 at the earliest.

Tuesday, the Vikings confirmed Jackson's rapid ascension of their depth chart and said he would start Thursday at Green Bay. Coach Brad Childress said Jackson has proved "a quick study," but he added a dose of reality to one of the most anticipated unveilings of a new starter in recent Vikings history.

"He'll give us the best chance to win right now," Childress said. "[But] I'm not foolish enough to think, having coached rookies before, that this won't continue to evolve. He's not going to be a finished product."

Jackson acknowledged his time came earlier than expected; it's likely Childress would have turned to Brooks Bollinger as Brad Johnson's replacement if Bollinger had not separated his left shoulder Dec. 3. Nevertheless, Jackson said it "feels good that [Childress] feels confident enough to put me in there." Jackson added that, "if you're playing good, there's no pressure," and he thanked Johnson for serving as a helpful role model this season.

"Brad has been so good for us and throughout his career," Jackson said. "I learned so much from him. Anything that you see me do on [Thursday] or throughout the year, it's because of me watching him and him helping me out so much."

Johnson, who was not available for comment Tuesday, took the news "just like the pro he is," Childress said. Johnson is expected to serve as the No. 2 quarterback Thursday night and in the season finale Dec. 31 against St. Louis, but his days with the Vikings almost certainly are numbered.

Meanwhile, players drawn into weeks of secrecy, intrigue and mixed messages seemed relieved Tuesday to see the drama conclude.

"We're all rallying around him," tight end Jermaine Wiggins said, "and we're going to do what we have to do offensively to help him out as much as possible."

Center Matt Birk said Jackson has displayed maturity beyond his status as a rookie, adding that the switch "doesn't really change a whole lot for me.

"Maybe just a different set of hands [under center]," Birk said. "He's a pretty level-headed guy. It's not like he's going through puberty here. He's a pretty cool customer, even being called into duty like he was on Sunday [against the New York Jets]. He wasn't scared, which is good. You can't be scared. You can't be tentative. You can't be afraid to fail. It seems like his head is in the right spot."

Jackson will become the fifth rookie quarterback to start an NFL game this season. The Vikings will have a more mobile quarterback with greater potential to complete deep passes, but Childress said his game plan is based on the Packers' defense rather than Jackson's particular skill set.

"You [change] a few things," Childress said, "but really, you are attacking their scheme of defense in Green Bay: The front they are playing, the coverage that they are playing with specific routes. All the while, you are mindful of what people do better than others. But it's not like you taper a complete game plan toward one quarterback or the other."

Under the tutelage of Johnson and quarterbacks coach Kevin Rogers, Jackson said he has added considerably to his knowledge of NFL defenses since the preseason.

"Right now, Jackson said, "I feel I can just go out there and play."

Childress will be evaluating his level of sophistication Thursday and against the Rams, hoping to determine if Jackson can enter the 2007 season as the Vikings' unquestioned starter.

"You are always looking to see time and distance," Childress said, "and how fast he is accelerating on the curve. Did he stay the same? Did he get worse? Did he get better? I have high expectations for him. He's prepared."

Kevin Seifert • kseifert@startribune.com