Normally in a situation where you want to modify/change an icon, you go to a "window," click on tools.......folder options......file types....and then scroll down to the program you're trying to work with. For example, I just changed my mp3 icons to another icon design.

Interesting.......I didn't see an icon for ZIP folders. I've never done this but you can try clicking on "new" (when you're on the "folder options" dialogue page, and put "ZIP" in the box, click on 'advanced' and make sure it reads "compressed zip folder" and hit OK.

If that works, and you end up with an icon for ZIP files, you can then use the "change icon" tab to whatever one you want to use.