Dim sInclude As String
 
Private Sub Form_Load()
    sInclude = "bcdfghjkmpqrtvwxy2346789"
End Sub
 
Private Sub Text1_Change()
Dim iTemp   As Integer
Dim sLetra  As String
Dim sTotal  As String
Dim iPos    As Integer
Dim bSetNew As Boolean
 
    For iPos = 1 To Len(Text1.Text)
        sLetra = Mid(Text1.Text, iPos, 1)
        If InStr(1, LCase(sInclude), LCase(sLetra)) > 0 Then
            sTotal = sTotal & sLetra
        Else
            bSetNew = True
        End If
    Next iPos
 
    If bSetNew Then
        iTemp = Text1.SelStart
        Text1.Text = sTotal
        Text1.SelStart = IIf(iTemp > 0, iTemp - 1, iTemp)
    End If
End Sub
 
 

'Por defecto la funcion solo filtra los numeros y el punto '.'
Public Function IsCharacterHere(ByVal sCharacter As String, Optional ByVal bCaseInsensitive As Boolean = False, Optional ByVal sFilter As String = "0123456789.") As Boolean
    If sCharacter <> "" Then
        If InStr(1, sFilter, sCharacter, IIf(bCaseInsensitive = False, Empty, vbTextCompare)) <> 0 Then
            IsCharacterHere = True
        End If
    End If
End Function
 
Private Sub Text1_KeyPress(KeyAscii As Integer)
    'Solo permite poner las caracteres alfabeticos del teclado... (Es caseInsensitive,da igual minisculas que mayusculas)
    If IsCharacterHere(Chr$(KeyAscii), True, "qwertyuiopasdfghjklzxcvbnm") = False Then
        KeyAscii = 0
    End If
End Sub