Play around with
Spy++[
^].
You could implement a global message hook, Spy++ can help you determine what to look for - Windows class, messages to monitor and so on.
The shell API provides many notifications:
http://msdn.microsoft.com/en-us/library/bb774198(v=vs.85).aspx[
^] - some which nearly fits the bill - like SFVM_GETTOOLTIPTEXT.
If you can get by using the notifications, you are in luck - the other approach is MUCH more complicated, and probably quite error prone - not even sure it will work alike for various versions of windows ...
Regards
Espen Harlinn