4
Okay I figured this one out -- I'm new to this whole thing, so use this hack at your discretion, but it seems to work.

Edit the following files:
function.php:
After
$glo_definition = $myts->makeTboxData4Show($glo_definition); add this line:
$glo_definition = $myts->xoopsCodeDecode($glo_definition, $allowimage = 1);
glossaire-aff.php:
After
$glo_definition = $myts->makeTboxData4Show($glo_definition); add this line:
$glo_definition = $myts->xoopsCodeDecode($glo_definition, $allowimage = 1);
glossaire-rech.php:
After
$glo_definition = $myts->makeTboxData4Show($glo_definition); add this line:
$glo_definition = $myts->xoopsCodeDecode($glo_definition, $allowimage = 1);
glossaire.php (for the marquee block):
After
$definition = $myts->makeTboxData4Show($myrow['definition']); add this line:
$definition = $myts->xoopsCodeDecode($definition, $allowimage = 1);
Note: this will only convert XOOPS code, I couldn't figure out a way to convert HTML. If you want to add more XOOPS code, check out the xoopsCodeDecode function in /class/module.textsanitizer.php.
Brad