You're right Helen....it was a caching problem. With a standard moodle theme it shows fine in both IE and Firefox, but with the College 1.5 Theme the lines overlap in both browsers. So, I'm back to it being a problem with the College 1.5 theme css.
Thanks for the great troubleshooting Helen...I'll check the site to see if they have already fixed this in the College 1.5 theme and, if not, I'll see if I can fix the css.
You're rigth...Firefox is excellent...I've installed it on all of our College computers...now if I could only get all my teachers and students to install it on their home computers