The PC version of the original Colin Mcrae Rally contains 2 secret cars and 4 secret tracks that can be unlocked only by using codes (the secret tracks and cars aren't available in the PS1 version). The codes can be found in the video, as well as on Gamefaqs' page of the game: www.gamefaqs.com/pc/196947-co...
Cars:
1.Toyota Celica GT4 WRC
2.Millennium 4 Rallye (fictional car)
Tracks:
1.Danger - Open Cast Mind
2.Mile High Parc
3.Retsil Lap
4.Trout Heights