To use them enter these in the game code menu found under Options.
4LAEYR10WLRC5 - Vehicle Set 1.
LNBMGDCLPDMF3 - Vehicle Set 2.
T0KVTQDLYM38G - Vehicle Set 3.
EAQ79LF4G37DB - All Liveries.
25ATEU26BWD0B - All Single Events.
9YME5A0H30HEJ - All Tracks.
R8RNQ7NP6M0DC - Championship.
To increase your average speed (stats), go for Hill Climb, Pikes Peak C (or BC) with a Toyota Tacoma.
To increase your maximum speed (stats), go for Hill Climb, Windy Point A, which is almost a long straight with some turns. Try using the Toyota Tacoma.
Unlock Colin McRae R4 Bonus Car and Unlock Ending videos
You'll have to finish in first place in all 66 events to get a 100% completion and unloc car and two ending video sequence as well.
When you are familiar with all tracks, accelerate hard on the straights and brake a good time in advance before a turn. Accelerate about halfway down at the beginning.