The Vikings decided to bring in Sage Rosenfels to compete with Tarvaris Jackson. Why they did it, maybe motivation for T-Jack.
Sage Fosenfels turns the ball over way to much to play a full season and lead a team to the playoffs, and nobody knows if he can play a full season. Rosenfels last year threw 6 TD's and 10 INT's in 6 games and a 2-4 record. He has thrown 21 TD's and 22 INT's over the last 2 years.
Jackson threw 2 TD's and 5 INT's in his rookie season, in his second season he threw 9 TD's and 12 INT's, then last year in 4 games he threw 9 TD's and only 2 INT's.
If Jackson continues to progress at the same pace he did last year I have no reason to believe why he can't lead the Vikings to the Super Bowl. It's very possible that Rosenfels could lead them to the playoffs next year, but Jackson seems to be the best overall option.