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either way, just install XOOPS in that folder, and the index.php (a new one, in the parent, not from xoops) should have a redirect system, like a http header, or a meta-refresh or something, don't need to use index.php from xoops...
.... home.php? what is that?
Or maybe I didn't understand you LOL
PD: if you want to move a working site, you only need to edit mainfile.php, don't forget to leave it in 444 when you finish