Hi TT,
It sounds as if you've created a "Border Line".
What I would suggest is first go to Tools/ AutoCorrect Options/
AutoFormat as You Type, and deselect the box that says "Border lines".
Then go to Format/ Borders and Shading, and under Borders, click
"none".
Hopefully this will help, it works for me in Word 2003.
Best of luck with this!
Karen