No more Fizzbuzz. How about Hello World instead?
Just a slight optimization: instead of evaluating the modulo twice just declare two booleans an evaluate them upfront.

Public Function Convert(ByVal number As Integer, _
                        Optional ByVal fizzDivisor As Integer = 3, _
                        Optional ByVal buzzDivisor As Integer = 5, _
                        Optional ByVal fizzWord As String = "Fizz", _
                        Optional ByVal buzzWord = "Buzz")

    Dim fizzState As Boolean
    fizzState = (number Mod fizzDivisor = 0)

    Dim buzzState As Boolean
    buzzState = (number Mod buzzDivisor = 0)

    If fizzState And buzzState Then
        Convert = fizzWord &amp; buzzWord
    ElseIf fizzState Then
        Convert = fizzWord
    ElseIf buzzState Then
        Convert = buzzWord
    Else
        Convert = number
    End If

End Function


Also you may not want to include as many newlines in the arguments as I did but you don't want a line over 200 characters long or use a horizontal scroll-bar.