It depends....
Most of the 3d models requiere alot of modding before they actual look good ingame(and work properly)
There are few tutorials arround but not one is 100% complete:
http://www.modthesims.info/showthread.php?t=96995You find some info here:
http://www.insimenator.org/index.php/topic,30891.0.htmlDo you have the texture files with the 3d model?
It could save ya some work.
I noticed you requested this on several sites, this will actual scare creators off.......
I am not making a car with the possibility some one else is going to beat me to it.....
Had a attempt once to write a decent tutorial, i will upload it here:
Note that it is far from finished but it will get you started!
http://www.insimenator.org/index.php/topic,107641.0.html