On my M400 i have two harddrives -both booting Vista and ONE -and only one- of them search wasn't working in Outlook 2007.

In doing some looking around it turns out the event log was giving me a clue that the Gatherer wasn't working correctly:

The content source <mapi://{s-1-5-21-38895556-1487699162-1270813805-26038}/> cannot be accessed.

Context: Windows Application, SystemIndex Catalog

Details:
The specified address was excluded from the index. The site path rules may have to be modified to include this address. (0x80040d07)

armed with this information it didn't take long for me to see this was a known issue -if you had installed an Office 2003 product on  top of Office 2007- which of course i had to do some VSTO demos.   Luckly the work around was quite easy: simply repair Office 2007 to reset the registery keys:

1.Exit all 2007 Office programs.

2. Click Start, type appwiz.cpl in the Start Search box, and then click appwiz.cpl in the Programs list.
If you are prompted for an administrator password or for confirmation, type your password, or click Continue.

3. In the Uninstall or change a program list, click Microsoft Office Version 2007, and then click Change.

4. In the Microsoft Office Version 2007 dialog box, click Repair, and then click Continue.