Hello again. I fixed the problem by comparing various template files with the original version of zen-cart and found that there was a missing "/>" (without the quotes) in the includes/templates/templates_default/common/html_header.php file. I added those 2 characters back to the file and the Internet explorer problem was fixed.

Couldn't say how those characters went missing, but I thought I'd pass on the answer in case someone else runs into this sort of problem.