You might be able to use the information from the following page for Word even though it is written for Excel VB script. Placed in your Word document's VB module it should be just a matter of figuring out how to trigger it.  It works great in Excel.

http://support.microsoft.com/kb/213360

Option Explicit
'Main Function
Function SpellNumber(ByVal MyNumber)
    Dim Dollars, Cents, Temp
    Dim DecimalPlace, Count
    ReDim Place(9) As String
    Place(2) = " Thousand "
    Place(3) = " Million "
    Place(4) = " Billion "
    Place(5) = " Trillion "
    ' String representation of amount.
    MyNumber = Trim(Str(MyNumber))
    ' Position of decimal place 0 if none.
    DecimalPlace = InStr(MyNumber, ".")
    ' Convert cents and set MyNumber to dollar amount.
    If DecimalPlace > 0 Then
        Cents = GetTens(Left(Mid(MyNumber, DecimalPlace + 1) & _
                  "00", 2))
        MyNumber = Trim(Left(MyNumber, DecimalPlace - 1))
    End If
    Count = 1
    Do While MyNumber <> ""
        Temp = GetHundreds(Right(MyNumber, 3))
        If Temp <> "" Then Dollars = Temp & Place(Count) & Dollars
        If Len(MyNumber) > 3 Then
            MyNumber = Left(MyNumber, Len(MyNumber) - 3)
        Else
            MyNumber = ""
        End If
        Count = Count + 1
    Loop
    Select Case Dollars
        Case ""
            Dollars = "No Dollars"
        Case "One"
            Dollars = "One Dollar"
         Case Else
            Dollars = Dollars & " Dollars"
    End Select
    Select Case Cents
        Case ""
            Cents = " and No Cents"
        Case "One"
            Cents = " and One Cent"
              Case Else
            Cents = " and " & Cents & " Cents"
    End Select
    SpellNumber = Dollars & Cents
End Function
     
' Converts a number from 100-999 into text
Function GetHundreds(ByVal MyNumber)
    Dim Result As String
    If Val(MyNumber) = 0 Then Exit Function
    MyNumber = Right("000" & MyNumber, 3)
    ' Convert the hundreds place.
    If Mid(MyNumber, 1, 1) <> "0" Then
        Result = GetDigit(Mid(MyNumber, 1, 1)) & " Hundred "
    End If
    ' Convert the tens and ones place.
    If Mid(MyNumber, 2, 1) <> "0" Then
        Result = Result & GetTens(Mid(MyNumber, 2))
    Else
        Result = Result & GetDigit(Mid(MyNumber, 3))
    End If
    GetHundreds = Result
End Function
     
' Converts a number from 10 to 99 into text.
Function GetTens(TensText)
    Dim Result As String
    Result = ""           ' Null out the temporary function value.
    If Val(Left(TensText, 1)) = 1 Then   ' If value between 10-19...
        Select Case Val(TensText)
            Case 10: Result = "Ten"
            Case 11: Result = "Eleven"
            Case 12: Result = "Twelve"
            Case 13: Result = "Thirteen"
            Case 14: Result = "Fourteen"
            Case 15: Result = "Fifteen"
            Case 16: Result = "Sixteen"
            Case 17: Result = "Seventeen"
            Case 18: Result = "Eighteen"
            Case 19: Result = "Nineteen"
            Case Else
        End Select
    Else                                 ' If value between 20-99...
        Select Case Val(Left(TensText, 1))
            Case 2: Result = "Twenty "
            Case 3: Result = "Thirty "
            Case 4: Result = "Forty "
            Case 5: Result = "Fifty "
            Case 6: Result = "Sixty "
            Case 7: Result = "Seventy "
            Case 8: Result = "Eighty "
            Case 9: Result = "Ninety "
            Case Else
        End Select
        Result = Result & GetDigit _
            (Right(TensText, 1))  ' Retrieve ones place.
    End If
    GetTens = Result
End Function
    
' Converts a number from 1 to 9 into text.
Function GetDigit(Digit)
    Select Case Val(Digit)
        Case 1: GetDigit = "One"
        Case 2: GetDigit = "Two"
        Case 3: GetDigit = "Three"
        Case 4: GetDigit = "Four"
        Case 5: GetDigit = "Five"
        Case 6: GetDigit = "Six"
        Case 7: GetDigit = "Seven"
        Case 8: GetDigit = "Eight"
        Case 9: GetDigit = "Nine"
        Case Else: GetDigit = ""
    End Select
End Function