[Soeren]

You can do it like this, it's how I handle it. There are more options but this works fine for me:

pawn Код:

public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
    if(!ispassenger) // Let others still enter the car as passenger, delete if you don't want that
    {
      if(GetVehicleModel(vehicleid) == 596) // The Vehicle-Model, change it to whatever you like
      {
         if(gTeam[playerid] != TEAM_COPS) // However you have defined your Team
         {
            new Float:X, Float:Y, Float:Z;
            GetPlayerPos(playerid, X, Y, Z);
            SetPlayerPos(playerid, X, Y, Z);
            SendClientMessage(playerid,0x63AFF00A,"You are not a Cop!");
          }
      }
    }
}

Hope I could help you!