_car = "XXXX" createvehicle getpos YYYY
where "XXXX" is the classname for the vehicle
and
YYYY is the name of the gamelogic
if you have problems with the positioning because of the gamelogic, use an empty marker
the line would then look like
_car = "XXXX" createvehicle getmarkerpos "YYYY"
notice getpos changes to getmarkerpos and the "YYYY" have quotation marks around them
Ideally this should be done only by the server, and if is the case you should be ok with the gamelogic.