[DaRealShazz]

Create variable:

pawn Code:

new pCars[MAX_PLAYERS];

Put this under the car spawning command:

pawn Code:

if (pCars[playerid] > 0) DestroyVehicle(pCars[playerid]);
PutPlayerInVehicle(playerid, CreateVehicle(modelid, Float:x, Float:y, Float:z, Float:angle, color1, color2, respawn_delay), 0);
pCars[playerid] = GetPlayerVehicleID(playerid);

You have to put in the parameters for CreateVehicle function.
Haven't tested, but it should work.