I had an epiphany while reading your story lol. Ok so they get the walker made, use it, but absolutely destroy all remnants of modern civilization. The survivors, AKA the people running the X001, then live off of the great machine, becoming nomads, wandering around picking up junk metal and supplies. Hundreds of generations go by, perhaps a couple of million years, if you want to be cool. Since the walker is self reparing, it doesn't age. The story goes on to describe the now almost extinct human race and the lives of the walker people. Since new plants and animals have emerged, life is a tad more hazardous than it is now. hmm. use it if you like =] oh an by the way...have you read any of the Bolo books? there kinda like this...

hey, wow i deffinately want a monolith, it would be quite handy but i would need a sean to drive it, ah well, a very good dtory keep at it!

hey, wow i want a walker x001 it seems really cool, this chapter has to have the highest body count ever even for you over 500,0,0 million dead, your mean to your characters, oh well still a cool story! keep at it, and upload some mister

Just a little question:
Is the X001 that much of a threat?
All you need to do is catch it in the blast of a small nuke, and once it tips over... Game Over. (It maybe on four legs, but it's really tall compared to it's width, leading to a high centre of mass. Not to mention it's a huge target, one that you can hardly miss.)
On a world where it is possible to deploy mini-missiles from larger missiles, a moderately large attack by a wave of 'multi-missiles' would easily over-saturate a defence system, with the chances of even one warhead closing to lethal range being very, very high.
In a way, it sounds like "Homeworld" (with the Mothership and all) but the capability of the X001 is, in truth, much worse. Space is big, it's 3-D, and the Mothership can move anywhere. On a planet, on a 2-D plane, once located, the X001 will find it very hard to avoid enemy recon, unless it can move very very fast and avoid spy satallites.
The way you have it now requires a quality of 'suspension of belief' on the part of the reader.