2
This is just a thought...
Install both XOOPS site in the same database (different database prefixes). In the admin site, which doesn't need registration, you can hack the cbb module to read the database of the other XOOPS installation, instead of the one of that installation.
you'd have to look for statements like:
$sql = "SELECT COUNT(*) AS total FROM
".$xoopsDB->prefix("bb_topics")." WHERE forum_id = $forum_id";
and change them to something like:
$sql = "SELECT COUNT(*) AS total FROM
xoops_client_bb_topics WHERE forum_id = $forum_id";
I did something similar to get xcgall to read from a coppermine installation...