Navigation Pane text in Word 2008 is essentially unreadable

When I view the Navigation Pane in existing do***ents , the text is
essentially unreadable. Specifically, the letters in each line in the
Navigation Pane are all squished up on top of each other. The only way
to get them to be readable is to redefine the Do***entMap style to
have expanded text by 5 points (!). Even then, it doesn't look like it
is meant to.

I have tried creating new do***ents, adding a few headings (styled as
Heading 1) and turning the Navigation Pane on. Same problem.

I am running Word 12.1.0 (080409) under OS X 10.5.3 on an Intel
MacBook with 2 GB of RAM.

I've searched this group and other places without success. Any help
gratefully received!