First go into the game and play a bit to earn a little extra cash, at least
$10,000.00 or so. Now sell your truck. Your should have somewhere near 
$40,000.00.

Look in your directory for the following file:
"C:\programs\Terminal Reality\4x4 Evolution\system\metal.ini"

..open the (metal.ini) file using notepad listed in your accessories 
folder in Windows. Now save the file in a temporary folder or on your
desktop. Go back into the game and buy a vehicle and some of the parts
you want. When your cash is low, do the following:

Exit the game and go back into your temporary folder and open the file
named metal.ini and look for a line that says:
Cash=(followed by a series of numbers and letters)

I think the string is specific to the your player profile.
Select the line and copy it. (now this is important only
select the line that says Cash=(and the string of characters
following the equal sign) not the entire file).
Now open the metal.ini file in your:

C:\programs\Terminal Reality\4x4 Evolution\system\metal.ini

and look for a line that says:
Cash=(followed by a series of numbers and letters)

Select that line and paste over it the line you copied from the previous
file.

Now save the file and exit notepad. Go back into the game and like magic
you just padded your wallet again. If you want more cash, like say enough
to buy one of race trucks, just sell your truck again and repeat all of 
the steps above. Remember every time you save the current:

C:\programs\Terminal Reality\4x4 Evolution\system\metal.ini

...your increasing the amount of cash you have. You can just keep 
doubling the amount of money you have by buying several trucks, 
pasting a new line in and then selling the trucks you bought. 
Saving that current file into your temporary folder and then buy
more trucks and parts and on and on and on until you have the 
amount of cash you want.

If you would like to get instant cash without doing this trick,
try putting in: "re25ykP*g*bCbqRqz*zb1xPz1P+" behind the cash=
line to get $2.5 million. (omit the quotes)