[color=darkblue]Option Explicit[/color]
 
[color=green]' diese Konstante enthält alle Buchstaben, die groß bleiben 
' sollen
[color=darkblue]Const[/color] ConvInCaptialLetter = "ralf"
 
[color=darkblue]Private Sub[/color] Text1_Change()
  [color=darkblue]Dim[/color] Text [color=darkblue]As String[/color], SelS _
    [color=darkblue]As Long[/color], SelL [color=darkblue]As Long[/color], I _
    [color=darkblue]As Long[/color]
 
  [color=green]' LCase wandelt den Text komplett In Kleinbuchstaben um
  Text = LCase(Text1.Text)
 
  [color=green]' aktuelle Markierung festhalten (StartPosition / Länge)
  SelS = Text1.SelStart
  SelL = Text1.SelLength
 
  [color=green]' Buchstaben ersetzen
  [color=darkblue]If[/color] Len(ConvInCaptialLetter) > 0 _
    [color=darkblue]Then[/color]
    [color=darkblue]For[/color] I = 1 To Len(ConvInCaptialLetter)
      Text = Replace(Text, Mid(ConvInCaptialLetter, I, 1), _
              UCase(Mid(ConvInCaptialLetter, I, 1)), , , vbTextCompare)
    [color=darkblue]Next[/color] I
  [color=darkblue]End If[/color]
 
  [color=green]' geänderten Text In Textbox zurückschreiben
  Text1.Text = Text
 
  [color=green]' Markierung wiederherstellen
  Text1.SelStart = SelS
  Text1.SelLength = SelL
[color=darkblue]End Sub[/color]

Viel Spass,
R@lf