I'm using Microsoft Word 2004 for Mac and just started having troubles with the horizontal ruler showing 13 inches even though the page set up is set at portrait and letter size. I've tried shutting down & restarting, changing margins on the document, making sure that the track changes isn't on. Help. (Please)

Well, I'm pretty sure you've probably already tried these things, but did you go into the Document Setup > Display and make sure that the display units are in inches? Also check under Page Setup and make sure that your Letter size is actually 11x8.5".