I'm having the same problem here. Outlook hangs for several minutes when receiving email. If I disable the Outlook/Exchange provider, the problem goes away. If I enable the Outlook/Exchange provider, the problem reappears.
I'm running Vista 64bit Ultima. Using the Windows Firewall, XAMPP, Ad-aware 2008 (Problem started before I installed Ad-aware). Outlook is part of Office Professional 2007, complete install.
Vista was a fresh install on March 30, a couple of weeks ago.
-JJ