Clones and copies of games have existed since the dawn of the industry so (unless they have trademarked elements that have been directly copied by Microsoft) I think they’re SoL on suing based on the content of the game; and the title "Scrap Metal" is such a common term that it would be difficult to argue that it infringed upon the trademark of "Twisted Metal". While it may seem similar to changing "Megaman" to "Megadude", and in practice it may be the exact same thing, legally there would be quite a distinction because of the commonality of the title.
Now, Microsoft may have (or may not have) copied the bulk of Twisted Metal when they made Scrap Metal but that is really not a problem unless it causes product confusion; and I don't really think it would, after all I didn't notice how similar the names were until I saw this thread.
