Open up config.cfg and change the following:
uset g_console "1"
Open the console by pressing "`" (the key to the left of "1")
Then you can use the following cheats:
cheat truck (n) - Change truck type, use number from 1 - 6
cheat skill (n) - Change your skill rating from 1 - 4
cheat dmeet - Meet all drivers
cheat contracts flow (n1)(n2) - Gives you licensed routes at skill 1 - 4 *)
cheat money (n) - Set the amount of money you want to have
cheat noticket - No more speeding or overweight tickets
*) Do this for each route in the management screen. Only the highlighted route will be affected by this cheat The first defines for which route you want a contract, the second defines the skill rating.