@Martijn: KB2458611 is part of office 2007 cumulative update Dec'10 (KB2479671). Note that that one might be pulled ATM due to issues (see http://blogs.msdn.com/b/outlook/archive/2010/12/17/issues-with-the-recent-update-for-outlook-2007.aspx)
@Mauricio: Never was (also not in Outlook 2010), and probably never will. One of the ideas of archiving is to keep your mailbox with recent/current mail as smooth and slick (i.e. small and fast) as possible. You can make this one available offline. Now what would happen if you made your 10 GB archive available offline and let Outlook keep it in sync with your online archive? Stress on network (initial sync), corruption, ..