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There are some themes available in the "Downloads" section here in Xoops.org. If you do a search with Google you'll bring up some other sites.
Most of these themes will not require templates, a theme basically consists of an index.html file, a few CSS files (for different browsers)and any images the theme needs. These are usually zipped or tarred (Unix compression program)for convenience, once unzipped or untarred, you will have a folder with above files in it, which you then upload to your /themes folder of your XOOPS installation.
Then you should be able to select it in your admin menu.