OK then, although you still didn't really explain the process you go through when installing a car, I'll try and give you some help.
If the Bruiser car your downloading is from RVZT :
HERE
Then please try and follow these instructions;
Double click on the zip file to open/view it in your default archive/extraction program.
If the cars have been packaged/zipped properly then they should have
Cars\Carname extraction folders when viewed in your archive/extraction program.
Click on or select the extraction option, you should now be asked where you would like to extract the files, if the program has a 'use folder names' option then ensure this option is selected/checked.
Now using the browse/navigation locate where your installation of ReVolt is, you wan't your main ReVolt folder, example :
C:\Program Files\Acclaim Entertainment\Re-Volt
Now extract in to that folder, using the Cars\Carname extraction folders your car should be placed exactly where it needs to be, example :
C:\Program Files\Acclaim Entertainment\Re-Volt\Cars\Bruiser
Assuming you have unlocked all the access to all the cars you should be able to select this car in the game.
Some zip files only contain the Carname folder or no folder information, so you will have to extract to the proper folder : C:\Program Files\Acclaim Entertainment\Re-Volt\Cars or actually create the carname folder before extracting directly in to that folder, just ensure the carname folder is the same one specified in the Parameters.txt of the car.
If you still are having problems, then please discribe the process you are doing and we may be able to tell you where you are going wrong.