Themes for older versions should still work with newer versions.
Have a look in Preferences / Display / Images to see if the theme has added any images there. If it has, but they aren't appearing on your toolbars (or wherever) then it's likely your toolbars (etc.) are not set to use the standard images (e.g. "Standard Toolbar Image").
i.e. If the theme is changing an image which nothing in your config is actually set to use, then it'll look like the theme does nothing. Configure things to use that image and you should see it on them.
See this FAQ for more about background images: HOW TO: Understand and Configure Background Images