I've read a lot of posts on other newsgroups (that I lack a
subscription to). Here's the solution that worked for me:
I have Outlook 2007 and am running Windows XP SP3.
In windows desktop 4.0 I would get an error that says "full preview of
this item is not available unless Microsoft Outlook is running." in
the preview pane of emails found from the search.
To be able to see them I did this in Outlook.
Tools> Trust center>Add-ins>
Ensure "Com Add-ins" is shown in the "Manage:" drop-down then hit the
A "Com Add-Ins' window appears.
Ensure that both "Microsoft VBA for Outlook Addin" and "Windows Search
Email Indexer" are checked.
(I suspect that only the "Windows Search Email Indexer needs checked)
Re-open Outlook and Windows Search.