http://www.gtagaming.com/downloads ab is site say koi bhi vehicle mod down karo us mod mein do files hoge dff or txd ab img tool say .dff or .txd file replace karo for ex cheetah.dff,cheetah .txd.
img tool use karne ka tarika
img tool open karo file main jao open karo gta3 par clic karo. samne list aegi. edit main jao find par clic karo gari ka naam likho for eg cheeah.dff search nxt ka butt press karo.cheetah.dff find ho jai ga phir cheetah.dff ko replace karo downloaded mod cheetah.dff day is hi tarha chhetah .txd file ko bhi find karo or usko bhi replace kardo .thx