hi icsjohn,
Try the following macro. It counts from the start of the selected range and doesn't care whether the current selection is more, or less, than the desired word count.
Code:
Sub Demo()
Dim i As Long
i = InputBox("How many words do you want to select?", "Word Marker")
With Selection
While .Range.ComputeStatistics(Statistic:=wdStatisticWords) < i
.MoveEnd wdWord, i - .Range.ComputeStatistics(Statistic:=wdStatisticWords)
Wend
End With
End Sub