Option Explicit
 
Dim Position As Long
 
Private Sub Command1_Click()
    If Position = 0 Then
        Position = InStr(1, UCase(txt_Text.Text), UCase(txt_Suchwort.Text), _
            vbTextCompare)
    Else
        Position = InStr(Position, UCase(txt_Text.Text), _
            UCase(txt_Suchwort.Text), vbTextCompare)
    End If
 
    If Position > 0 Then
        txt_Text.SetFocus
        txt_Text.SelStart = Position - 1
        txt_Text.SelLength = Len(txt_Suchwort.Text)
        Position = Position + Len(txt_Suchwort.Text)
    Else
        Position = 0
        Call MsgBox("Suche beendet", vbInformation, "Suchergebnis")
    End If
End Sub
 
Private Sub txt_Suchwort_Change()
    Position = 0
End Sub