When you perform a search for a file in Windows XP. The default setting is for XP to ONLY return files in the “Search Results” pane – when they are registered file types to a program on your PC.
In other words if you are looking for a file that is NOT registered with an application on your PC, it will not be found using the default search settings. However, you can turn off the default by a quick Tweak of the registry!
Open the Registry editor (type regedit from the Run command) and navigate to:
HKEY LOCAL MACHINE\SYSTEM\CurrentControlSet\Control\ContentIndex
Double-Click the value named: FilterFilesWithUnknownExtensions and change the value from 0 to 1
Exit the registry editor and reboot!