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It's hard to find players who make a difference in the National Football League.

In free agency, they cost a lot of money. Or it requires a 13- or 14-loss season to get one. More than anything, though, it requires luck and smarts. There are plenty of good players available, it's just a matter of finding the right fit.

Last year, the Saints made the biggest gamble and won when they signed QB Drew Brees. Coming off shoulder surgery, Brees came to the Saints with no guarantees and ended up throwing for 4,418 yards and 26 TDs.

The Dolphins had first crack at Brees but decided to shy away. Instead, they traded for Daunte Culpepper, figuring a knee injury is less risky for a quarterback in the long run than a shoulder problem. You saw the results. The Dolphins finished 6-10, coach Nick Saban left for Alabama and Culpepper is trapped in Miami until a grievance resolves how he exits -- either by trade or waiver wire.

Another difference-making move was the Steve McNair trade of last year. The Ravens have been known for their great defense that asks for just a little bit from the offense. McNair did just that. He threw for 3,050 yards and 16 TDs and, more importantly, provided enough big plays on offense to help the Ravens win the AFC North with a 13-3 record.

Training camp is the first true test of how a new player fits in. Brees and McNair made their presences felt in camp. Now it's time to look at five players who could be impact players in 2007. It's not as though these five were the five most expensive free agents or cost the most in trades, but these five players are the ones who could turn around the personality or the strategy of a team.

1. Trent Green, quarterback, Miami -- Can he be this year's McNair? It's possible. Green comes to the Dolphins for what will probably end up being a fourth-round draft choice, and coach Cam Cameron is happy to pay that price if Green can complete somewhere between 62 percent and 65 percent of his passes and have a quarterback rating of 90 or better. Cameron's offense is based on efficiency and accuracy, and Green is an expert at both. No current quarterback has spent as much time in the Mike Martz-Norv Turner system as Green, who learned it back in his Redskins days when Cameron was the quarterbacks coach.

The question facing Green is his durability. Last year, he suffered a major concussion in the Chiefs' opening game and missed half of the season. Though the Dolphins still have questions along the offense line, Cameron's instructions to Green will be to get rid of the ball before getting hit. Despite the controversy of not taking Brady Quinn in the first round, the Dolphins tried to give Green some quick targets -- Ted Ginn Jr. at wide receiver and Lorenzo Booker out of the backfield. The goal for the Dolphins is to get scoring into the 20s. Despite Culpepper's strong arm, the Dolphins averaged only 16.3 points per game last year.

2. Adrian Peterson, halfback, Minnesota -- Peterson's showing in training camp could dictate the style of offense called by coach Brad Childress. If Peterson runs like a younger version of Larry Johnson, the Vikings could be a run-first team. They have a great one-two punch in Chester Taylor and Peterson. Taylor was among the rushing leaders during the first couple of months last year but wore down under the pounding. The combination of Peterson and Taylor could instead wear down defenses. Their effectiveness should be evident in training camp, and they'll be running behind a talented offensive line. Matt Birk is healthy again at center, and Bryant McKinnie and Steve Hutchinson will have better communication on the left side of the line.

A good running game could also make it easier for QB Tarvaris Jackson. The decision to start Jackson is one of the shakiest in the league. It's not that Jackson isn't talented -- he is. But he is also very raw. If the Vikings can come up with a running game that allows him to throw fewer than 30 passes a game, Jackson could be the surprise quarterback of the season.

3. Randy Moss, wide receiver, New England -- The only thing fans need to see at training camp and in the preseason is Tom Brady firing high, long, arching passes that Moss snatches in the back of the end zone. Moss doesn't have to catch 80 passes to be a success for the Patriots. He just has to score touchdowns, which is his specialty. Brady does a great job spreading the football to all of his receivers. Unlike Terrell Owens, Moss understands he doesn't have to catch every pass for a team to win. Sure, he got bored in Oakland. The Raiders didn't win and they didn't do a good job of getting the ball to him. Brady will have games in which he will throw only two or three times to Moss, but if those catches become two or three touchdowns, the trade -- which, for just a fourth-round pick, was a bargain -- will be one of the major success stories of the season and could result in a Super Bowl ring. Unlike T.O., who is all about himself, Moss made a sacrifice to become a Patriot. He took a $7 million pay cut. Try getting cab fare from T.O.

4. Willis McGahee, halfback, Baltimore -- Jamal Lewis was the perfect back for years in Baltimore. He wore down opposing defenses with his big, fast body, helped the offense control the clock, score a few points and then let the Baltimore defense do the rest. But the organization wanted a different look, and McGahee will give Brian Billick the ability to spread the field. The transition begins in training camp. Even though McGahee caught only 18 passes last year, he is expected to be more of pass-receiving presence than Lewis. The change is perfect for McGahee. He's ideal in a one-back set. Lewis loved running behind fullbacks, but McGahee doesn't care. He's a physical, downhill runner. Without the fullback on the field, Billick can experiment with more three- and four-receiver sets. The Ravens have been drafting talented young receivers in the past couple of years, but they didn't see the field as much because the Ravens ran so many two- and three-tight end sets. Watch McGahee in camp to catch a glimpse of Billick's plan for the offense.

5. Jeff Garcia, quarterback, Tampa Bay -- Coach Jon Gruden has been looking for a new Rich Gannon for years. When Gannon went from Kansas City to Oakland (when Gruden coached there), the Raiders went from an average team to a Super Bowl contender. Gannon was a fiery leader and acted like an NBA point guard in distributing the football. Gruden wants something similar from Garcia. The Bucs have weapons but haven't gotten the most out of Cadillac Williams and Michael Clayton in the past two years, partially because of all the question marks at quarterback. Garcia's job is to make everyone perform better. Last year, Garcia stepped into an Eagles offense that needed more of a running presence for years and made enough handoffs to get the Eagles back on top of the NFC East. Garcia's can't be asked to carry a team, but he's smart enough to know he can use the talent around him to accomplish his mission.

John Clayton is a senior writer for ESPN.com.