I am sorry for these problems. Since you noticed that B&W seems to be working fine if you have an empty mailbox, I think the problem is somehow related to the large PST file. Can you run a Detect & Repair job over that PST file (from the Outlook Help menu), then restart Outlook and see if B&W works better?
do you mean the Help-->Office Diagnostics? If so, I have run both the "Compact Now" on the pst, and also the Office Diagnostics (which didnt find anything wrong)
one other note, even with an empty mailbox (except for 2-3 messages), B&W still crashes Outlook if i delete an email in a search folder.