OOPS!!!
Read your request incorrectly. I first read it as 600 letters.
Here's the correct answer for word count...
Private Sub TextBox1_Change()
Dim iWordCount As Integer
iWordCount = 600
If Len(TextBox1.Value) - Len(Application.WorksheetFunction. _
Substitute(TextBox1.Value, " ", "")) > iWordCount - 1 Then
TextBox1.Value = _
Left(TextBox1.Value, Application.WorksheetFunction. _
Find("~", Application.WorksheetFunction. _
Substitute(TextBox1.Value, " ", "~", iWordCount - 1)))
End If
End Sub