In the MEMBERINFO template of your style, you will find the tabs list.
<div id="profile_tabs">
$template_hook[profile_left_first]
$blocks[aboutme]
$blocks[visitor_messaging]
$blocks[stats]
$blocks[friends]
$blocks[infractions]
$blocks[contactinfo]
$template_hook[profile_left_last]
</div>
Just change the order of any $blocks[].
Dont change the $template_hooks as they need to remain in position first and last.
Thats actually a great idea since it could limit visitor message posting,
(first thing people want to do when seeing an input box is post something.)
Getting that block out of the way by default would keep the posting to the forum, in some cases.
This is only a theory. lol