11
using my own implementation of a multi-site hack, i've been able to achieve a multi-site install from a single core installation
my shared hosting environment stores each website in a folder, each site/domain folder stored 'beside' the others
username
|__ DOMAIN1.COM
|__ DOMAIN2.COM
etc.
i installed my modified XOOPS into domain1.com, configured it and whatnot, then created symlinks into domain2.com, symlinking *ALL* files except mainfile.php, cache, templates_c, and then i modified includes/cp_header.php, modules/system/admin.php, so that the admin side functions properly (otherwise, the wrong files would often get 'included')
there's a prefix used for the shared tables (i.e.- xoops_all), and then each site has it's own individual prefix (i.e.- xoops_, xoops1_, xoops2_)
this required no modification to apache configuration files, allows me to run sites that function separately of each other, share the tables that i want to share, and upgrade the XOOPS core or XOOPS modules for all sites simultaneously (the physical file part of the upgrade)