10
you might still be able to recover some or most of your files, depending on what has been overwritten...
if you were using a theme that you had to download and then upload to your site from elsewhere, then it is probably still in your themes folder, as it wouldn't have been overwritten.
if you were using a clone of your original templates, they may still be in the templates_c folder...just download the whole thing
if you haven't overwritten the database, try a tool like phpmyadmin to back up your database...
download everything in the modules folder as well...
then you can just delete all your old files, upload the latest xoops, install it, upload your old theme and set it as active, upload and install your old modules from scratch, just leave the ones that don't work for now, then upload and see if you can get your templates clone to work, set the clone as the default...then try and reinstall the db with phpmyadmin...
you can download phpmyadmin here:
http://www.phpmyadmin.net/home_page/index.phpit's not as hard as it looks to back up a db...search for tutorials on the web on this...
but, all that said, there may be another way to continue with the site upgrade that doesn't require you to do this...
hope that is some help!