It was purchased at our local Wal-Mart and was pre-installed by the retailer.
If I have to have them re-install Office, will I end up being without my laptop or do you know if that's something they can do right there in the store?
Since it was purchased from a retailer, Wal-Mart would have to be an authorized reseller. Meaning, not only would Office 2007 (Including Word) be pre-installed there has to be media with it. You purchased it, you're entitled to an actual CD copy of the software you purchased, pre-installed or otherwise.
Presuming you've gone through all the CDs you were given along with the laptop, and none of them are Office 2007, then I would go back to Wal-Mart and say WTF?
Sometimes software is sold online and unless you request the media, and for a small cost, you can get the media. But I don't believe that is the case with Office 2007. Either you, or Wal-Mart has the CD or can get it for you.