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I'm sure you like the design and layout of your site, but if you want you can install XOOPS completely and then make a theme tha works just like the current site that you have now. As far as I know there is not an easy way to put XOOPS into a static html page as XOOPS is dynamic and the architecture is completely different. I'm sure there is a way, but I think you would benefit more if you were to just intall it from scratch and make your own theme.