Messages

I recently bought the game and obviously tried installing some bikemods. I followed the tutorials right, I assume, I made the bikes folder with the subfolder of the normal default bikes. I then added the other bikes to that folder. I tried unraring them and making folders for them like normal bikes, or just putting in the .pkz files. no matter what i do, each time I select the category to select the bike, the game freezes and crashes on the message saying "core.exe has stopped working." I have no idea how to fix this and can't find a fix. Any ideas?