If you take that on a real trail, within a mile or two, you'll simply be out your $139+shipping and have nothing to show for it--unless the catostrophic failure also leads to serious injury in which case the only think you'll have to show for it will be broken bones and medical bills. Oh, yeah, you wont even have enjoyed the mile you rode before it/you broke.
I have seen the above scenario multiple times. I've never seen anybody do serious mountain biking on a Wal-Mart (or comparable) bike and not suffer the consequences. Better to save your cash for something you will enjoy (even if it's not mountain biking) than to simple waste it in this manner.
I know we may come across as horrible bike snobs, but non of us will assert that you have to spend 3 grand to get into the sport either. In my experience, the cheapest you can get a new, trail worthy bike is around $500 and that won't be a full suspension either--which is certainly okay; even though I have a nice fully, I still have the first hardtail I ever bought and ride it regularly, enjoying every minute of it.
If budget is a serious concern, keep your eyes open for a decent used bike--just bring along a knowledgeable buddy before buying who can help you determine proper fit and the integrity of the bike itself.