Modify a shortcut to the game's executable by adding -cheats -funlabs to the command line. You can also attempt to start the game via MSDOS using this command in the game's directory:

mostwanted.exe -cheats -funlabs

Once that's done, hit the TIDLE key to drop a developer console and start cheating!

godMode (0) - God mode off
godMode (1) - God mode on
godModeTeam (0) - Team god mode off
godModeTeam (1) - Team god mode on
noclip (0) - clipping off
noclip (1) - clipping on
mw_failmission (0) - fail mission objectives off (never lose)
mw_failmission (1) - fail mission objectives on
mw_winmission (0) - win mission objectives off (never win)
mw_winmission (1) - win mission objectives on
mw_showhud (0) - HUD display type 1
mw_showhud (1) - HUD display type 2
mw_showhud (2) - HUD display type 3
mw_aiDisableThink (0) - AI off
mw_aiDisableThink (1) - AI on
mw_aiDisableAct (0) - AI cannot move off
mw_aiDisableAct (1) - AI cannot move on
mw_givealllevels (0) - all levels selectable off
mw_givealllevels (1) - all levels selectable on