I updated the Windows Desktop Search engine on my XP laptop before I applied the Office 2007 Technical Refresh. I thought it might have been a bit of a fluke but the related cached mode crashes seemed to disappear once I had upgraded the engine.
I think you are required to install the new build with the technical refresh of Office 2007 Beta 2, so it is a good idea to grab KB
917013 if you are going to run Outlook/Office 2007 on an XP machine. The engine is already built into Vista.
This would also explain why Outlook 2007 Beta 2 would crash under XP with cached mode enabled and wouldn't crash with Vista because the desktop search engine in the versions of Vista I ran were already many builds ahead of the technology preview for XP.
Case closed, I suspect.