C:\Users\(Sign on Name)\AppData\Local\Microsoft\Outlook
That's the default location that Windows 7 stores an Office 2007 Outlook file.
Your XP machine might not be able to access it (thus getting a blank search), because of the higher security settings of 7. See if you can browse there without getting any security warnings.
(The C would be the D for your search if I'm reading your post correctly)