[Iain M]

Edit the memberlist.css template.

Replace

#memberlist_table td.joindate,
#memberlist_table td.postcount,
#memberlist_table td.lastvisit,
#memberlist_table td.reputation {
	text-align:{vb:stylevar right};
}

With:

#memberlist_table td.joindate,
#memberlist_table td.postcount,
#memberlist_table td.lastvisit,
#memberlist_table td.reputation {
	text-align:{vb:stylevar center};
}