Chicago hasn't lost at Lambeau since 2003, and Lovie Smith has never lost at Lambeau as a head coach, so it's obviously a big monkey on the Packers' back. Football Outsiders says the Packers are the 7th best team in the NFL (seriously) and it's all because the NFL is "kinda good" this season:

"Right now, 16 different teams are either 6-3 or 5-4. That's half the league! With so many teams hovering around "kinda good," only three teams are better than 6-3, and only three teams are 4-5. By comparison, last year at this point nine different teams were 4-5...

Below the top three, things begin to diverge from conventional wisdom. The Packers may only be 4-5, but they rank seventh in DVOA, basically tied with the 7-2 Panthers. (They lost to the Vikings, and moved up three spots anyway because the system thinks they outplayed Minnesota by a small amount.)"

I guess that shows how important the quarterback is to their system. The Packers were outplayed by every Viking not named Gus Frerotte, and Frerotte played so badly that he almost made up for all the good work from his teammates.

While the Packers are clearly the best 4-5 team in the NFL, Chicago is one of the best 5-4 teams:

I really want to focus on the special teams rankings because when the Packers got crushed last season in Chicago 35-7 it was because of special teams. P Jon Ryan dropped one snap and had two other punts blocked. That was a unique game because of the freezing cold weather, but it still was a blowout because the special teams were awful. This season, Chicago's special teams are below average and one reason is that KR Devin Hester is not the same guy he was in 2006 and 2007. 

Looking at QB Kyle Orton, he appears to be having a season similar to Tennessee's QB Kerry Collins. Orton is better, but, just like Collins, he's playing it safe and not turning the ball over. Orton has 8 turnovers (fumbles and INTs) in 8 games, but 4 of them happened in the game vs. Philadelphia. He's had no turnovers in 5 of the 8 games he's started. Collins didn't have a great game against the Packers, so I don't expect Orton will be great either. But just like Collins, he won't turn the ball over either.

RB Matt Forte isn't having a great season, but he's been playing as well or better than three backs who killed the Packers this season (Marion Barber, Michael Turner, and Earnest Graham) so he should have a 100 yard game if Chicago can take the lead or keep it close.

Chicago's run defense is outstanding, so RB Ryan Grant should not be a huge factor in the game.

Chicago's pass defense is struggling. They compare to teams like Atlanta and Indianapolis, and QB Aaron Rodgers played well against both of those teams.

In all four of the Packers' wins, they built leads of over 10 points and managed to hang on for the win. Only Detroit managed to retake the lead, and the Packers had to come from behind to beat them. But not every team is as bad as Detroit. To win this game, the Packers have to get an early lead from their pass offense or their special teams and make Chicago throw the ball into the teeth of the Packers' outstanding pass defense.