I suppose you could use the SendKeys statement:
Code:
Private Sub WebBrowser1_DocumentComplete(ByVal pDisp As Object, URL As Variant)
    WebBrowser1.SetFocus
    SendKeys "^f", True 'popup the find dialog
    SendKeys "TheTextToSearchFor", True 'fill the dialog
    SendKeys "~", True 'do the first search
End Sub
Good luck!