Make sure that your postbit has the template hooks in it. Custom styles, especially for older versions may not have them. This mod requires the following lines in your postbit or postbit_legacy template, depending on which you use:
$template_hook[postbit_userinfo_left]
$template_hook[postbit_userinfo_right]
$template_hook[postbit_end]
If your postbit template doesn't have these and you don't know where to put them, you can add
$WWU002_rankblock
under the username and
$WWU002_statblock
under the postcount to add the stuff for this mod manually. With the manual mods, none of the postbit controls in the options will work, however.
To see the activity statistics page, go to the
Activity Top Activity Page section in the options and make sure the top two options are set to yes, then click the "Stats" link in the navbar. If your navbar doesn't have template hooks, the url will be like
http://zelaron.com/forum/index.php?do=activitystat
but with the path to your forum index. You'll need to manually put it somewhere.
I highly recommend that you update your style/get a style that has template hooks, as I suspect most vb3.7 mods will require them.