Trading Cards are unlocked during gameplay when you complete various goals in the game, below is a list of the challenges and what is unlocked accourding to what colour award you receive
Qualifying for a race on pole
Bronze: Jaques Lazier - Video Clip
Silver: Helio Castroneves - New Car Livery
Gold: Sam Hornish Jr - Nothing
Winning a 10 lap race
Bronze: Arie Luyendyk - Create your own team
Silver: Gil de Ferran - Nothing
Gold: Al Unser Jr - New Car Livery
Winning a quarter lap race
Bronze: Scott Sharp - Viedo Clip
Silver: Jeff Ward - Nothing
Gold: Robby McGehee - New Car Livery
Winning a full distance race
Bronze: Eliseo Salazar - New Car Livery
Silver: Shigeaki Hattori - Video Clip
Gold: Airton Dare - Nothing
Completing Masterclasses
Bronze: Richie Hearn - New Car Livery
Silver: Felipe Giaffone - Nothing
Gold: Sarah Fisher - New Car Livery
Winning the IndyCar Series
Bronze: Robbie Buhl - Nothing
Silver: George Mack - Video Clip
Gold: Laurent Redon - Nothing
Qualifying for the Indy 500 on pole
Bronze: Rick Treadway - Video Clip
Silver: Alex Barron - Nothing
Gold: Eddie Cheever Jr - Video Clip
Winning the Indy 500
Bronze: Buddy Lazier - Video Clip
Silver: Billy Boat - New Car Livery
Gold: Anthony Lazzaro - Nothing
By setting a lap record
Bronze: Budy Rice - New Car Livery
Silver: Tony Renna - Video Clip
Gold: Dan Wheldon - Nothing
Winning a race with AI set at 100%
Bronze: Homestead Miami - New Car Livery
Silver: Phoenix - Nothing
Gold: California - New Car Livery
By finishing a race
Bronze: Nazareth - Create your own driver
Silver: Richmond - Nothing
Gold: Pikes Pike - Video Clip
Winning all races in IndyCar Series
Bronze: Kansas - Nothing
Silver: Nashville - Video Clip
Gold: Michigan - New Car Livery
By winning the hard charger award
Bronze: Kentucky - Video Clip
Silver: Gateway - Nothing
Gold: Chicagoland - New Car Livery
By collecting all of the cards
Bronze: Texas - New Car Livery
Silver: Indianapolis - Nothing
Gold: Borg-Warner Trophy - New Car Livery