Quote:
I'm not sure if the subdomain reference (username.xoops.org) could be handled in this manner.
You just need a hosting account with Dedicated IP. Then you redirect your subdomains to your domain. You should have the option for use multicard subdomains so you don´t have to create all the subdomains by hand.
Example: redirect *.yoursite.com to www.yoursite.com
Then you need a script included on your mainfile.php to read the PHPSELF and extract the subdomain name. If the there is a name (subdomain) in the URL then you match it against your users database and get the corresponding UID. Having the uid you just need to redirect the page. No need for htaccess this way. :)