1.) core installation on same server
2.) symlinks created from each subdomain, excluding cache & uploads folders
3.) separate MySQL database for each subdomain - created from phpmyadmin, not XOOPS installation
4.) requires a few core and module hacks
Advantages:
- Performance isn't affected by symlinks
- only have to update one set of core files & saves server space
- separate database allows completely different settings and templates for each subdomain
- can create separate cpanel admin access to each subdomain
Disadvantages:
- core hacks!!!
- my web host disallows symlinks from separate domains even tho they are on the same server, so I can only use on subdomains
Bottom line is that it can be done, but requires pretty good understanding of XOOPS/PHP code.