3
Hmmm
First of all, it should work OK on a mac. All files in modules should be PHP and/or HTML which are platform independent.
To change your logo file, replace the image file in your selected theme with the image of your choice. Make sure it's the same size and image type as the original one or change the theme.html file to accomodate the changes.
Also, make sure you have selected "yes" in the "Update module template .html files from themes/your theme/templates directory?" part under system admin>preferences>general preferences.
With the module problem: Make sure you only upload the actual module folder. Some modules have extra folders in the zip file with the module folder as a subfolder. Make sure you read any instructions that come in the zip file to be sure.