I'm not much of a horror movie fan, but I do enjoy a good zombie movie (as long as its one that doesn't take itself too seriously). If you invite me over for Halloween, make sure you've got a copy of Shaun of the Dead or Evil Dead II around, just so we can laugh.
But zombies are real, and those of us who live in project-land, are all too familiar with zombie... projects. They live on, well past their day of expiration. Despite their slow, shambling appearance, they are very difficult to run away from. Removing the head is just about the only way to kill one.
Seriously, how do you kill a zombie project? In a phrase, not easily.
A zombie project usually lives only through the will of someone who isn't doing the daily drudgery and toil that keeps the project upright and shambling along. The best way really is to separate that driving will from the dead body of the project. Sometimes, that just isn't an option. Either you don't have a sharp enough weapon (your argument is dull) or you just don't have the strength to get it done on your own (weak level of organizational influence).
Trying to convince the person driving a zombie project forward is often a difficult proposal. For some reason, these individuals have convinced themselves that there is value to be had in this project reaching completion. It doesn't mean that the project's completion will bring value to the organization; it may mean value only to the person driving the project, but they see value there somewhere. You have to recognize that there is some kind of perceived value there, even if you can't see it.
And maybe that is the problem, too, that you just can't see the value. It might not be that the project is a zombie project, just one that's shuffling along arthritically. No, that's not healthy either, but maybe the project has to go that slowly in order for the rest of the organization to see its eventual value. Taking the time to verify if you're being chased by a zombie or just by some elderly project is time well spent.