Althought I'm testing on Linux RH9, I'm unsure IIS could be the culprit. We usually create content using Dreamweaver and upload them into Moodle without any hassle.
How do you upload the files?. It is better to zip them all togheter, upload the .zip, expand inside Moodle, the link single files as "uploaded resource".
Also, in Dreamweaver it is surely better to use relative paths instead of absoluthe paths.
Hope this help