Get Rid of Table Gridlines
The Problem:
I chose Table 
Hide Gridlines, but they're still hanging aroundeven through the Table menu now has the Show Gridlines command instead.
The Solution:
Here's another reason why Microsoft isn't renowned for its design brilliance. What you're seeing are actually the text boundaries for the table. You're seeing boundaries for the page's margins as well, aren't you? Choose Tools Options, click the View tab, and uncheck the "Text boundaries" box. That'll do the trick.