There is no way that developers of the game have provided to do that.You can use third party applications or saved files to do that.
How to do:
SAVED FILES :
Google for 100% saved game for gta vice city and try to find a reputed website to download the file.
Then copy the files to the users files in My documents.
Run the game and Run the saved game.Before hand you need to delete all the files other than the 100%.
make the backup of the files you are deleting.
Trainer:
There are trainer available by which you can modify the game and different features can be unlocked.
Download them use them to do so.
Use them after reading the instruction.
Always check the comments before installing as it can be a virus.
You must face all the challenges given by the creator to unlock all the legendary cars on cars.
You unlock levels one at a time. You unlock the next one after you beat the previous one.
all you have to do is unlock all the puzzle mode levels in plants vs zombies
SCORE is the code to unlock all the levels.
You have to beat all of the levels and then you get extra levels when you beat it.
unlock all levels zuma revenge
Beat the one before it...
NO!
Matrix
I don't know. there could be a cheat I think you unlock them by racing the cars.
UNLOCK ALL THE LEVALS!!!!!!
to unlock all cars when you go to the main screen press the buttons... L1, L2, R2, R1, and X.