Could be done using two standalone installations of wordpress,
and not actual zencart mod..then use The Loop at
http://codex.wordpress.org/The_Loop
to call posts from those WP installs into an ezpage or
define main page..
Wordpress integrated into zencart, via mod, can slow down
site/store performance.
Alternatively, why not use a forum..only one need be installed,
with different topics per his/her main subjects..
PHPBB 2.0* has a script facility for calling posts into a block outside
of actual forum..did have such a block somewhere that fitted
into zencart sideboxes...
HTH