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Yeh, unzip the folder on your computer and upload the theme to the themes folder....then go into main prefrences and you can set the default theme...
If you are going to be making changes to the theme after this process...make sure you also set update templates while you make the changes, so you see them happen....that's if you need to edit what it looks like....
Please read the FAQ's, XOOPS Documentation, and use the search alot...