If it is just Mcs and Macs you wish to capitalise then this should do it. However not all suffixes are capitalised. Macdonald is also valid.
[VBA]Option Explicit
Option Compare Text

Private Sub TextBox1_BeforeUpdate(ByVal Cancel As MSForms.ReturnBoolean)
Dim t
t = TextBox1
If Left(t, 2) = "mc" Then
t = UCase(Left(t, 1)) & "c" & UCase(Mid(t, 3, 1)) & Right(t, Len(t) - 3)
ElseIf Left(t, 3) = "mac" Then
t = UCase(Left(t, 1)) & "ac" & UCase(Mid(t, 4, 1)) & Right(t, Len(t) - 4)
Else
t = UCase(Left(t, 1)) & Right(t, Len(t) - 1)
End If

TextBox1 = t
End Sub
[/VBA]