I don’t know if there is an API there for it, but if you search in Windows for an unlikely string, say "zxcvbnm", then search the registry, and then in XP you will see it under one of the folders in:
HKEY_CURRENT_USER\Software\Microsoft\Search\ACMru
along with your other search strings. I assume that this registry location may vary between versions of Windows.
Windows 7, MSDN .