Tooltips are tricky with QTP. I have found that you can use mouse overs in conjunction with a property grab via descriptive programming. Please see my overview below which will give you an idea of how to approach this:

'There are a couple of ways to move the mouse to an object. One is with the DeviceReplay, and the other is with a direct mouse move.

'Example 1
Set obj = CreateObject(''Mercury.DeviceReplay'')
obj.MouseMove x, y

'Example 2
Window(''TestApp'').WinObject(''icon1'').MouseMove 22,15

'Next, follow the mouse movement with a delay and then a text capture using descriptive programming

Wait 2 '(delay to allow tooltip to appear)

' Capture the text of the tooltip object
txt= Window(''nativeclass:=.*tooltips_class32.*'',''index:=0'').GetROProperty(''regexpwndtitle'')
msgbox txt

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'If the object is web-based, then you can use something like the following:

Browser(''Browser'').Page(''Page'').Link(''Link X'').MouseOver
' Wait a second to allow the tooltip to be displayed.
wait 1
' Capture the text of the tooltip object

txt= Window(''nativeclass:=.*tooltips_class32.*'',''index:=0'')
MsgBox txt