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If I understand your question you want to have an index.html page as your default with links leading to Xoops? To do this you without redirects you can install XOOPS in a folder on your server. All the XOOPS folders and files need to be uploaded to this folder. Name the folder anything you wish, XOOPS will recognise the path during install.
After the files are upload type in your browser:
http://www.mysite.com/myfolder - this will run the XOOPS install
If I have not got the gist of your question post again..