checks if the String consists only of letters (A-Z, a-z) or not

IsLetter.bas

'source: http://techniclee.wordpress.com/2010/07/21/isletter-function-for-vba/
Function IsLetter(strValue As String) As Boolean
    Dim intPos As Integer
    For intPos = 1 To Len(strValue)
        Select Case Asc(Mid(strValue, intPos, 1))
            Case 65 To 90, 97 To 122
                IsLetter = True
            Case Else
                IsLetter = False
                Exit For
        End Select
    Next
End Function