[kh99]

If you create a plugin using hook location init_startup and code like this:

$new_datastore_fetch[] = 'userstats';

The you should be able to use {vb:raw vbulletin->userstats.numbermembers}

If you want the number formatted with commas, then you need another plugin. Maybe at hook showthread_complete and code like:

$numbermembers = vb_number_format($vbulletin->userstats['numbermembers']);
vB_Template::preRegister('SHOWTHREAD', array('numbermembers' => $numbermembers));

and then in the template use {vb:raw numbermembers}.