This topic should cum to attention for skilled GTA modders if they are interested. Someone should make the War Of The Worlds tripod machine. Let it move around realistically and shoot rpg rockets down at civilians and cars. Even better: make multiple machines to spawn and invade the city. It would make a great alien invasion film for GTA 4. Perhaps Machinima editors can present it.
I know it's very tough to mod at this high level, but it would be one of the most epic mods ever made for GTA, and it will possibly support one of the most epic films for GTA.