Ctrl +C (copy) and Ctrl +X (cut) are Windows shortcut keys rather than Excel
specific and I don't think its possible to disable them in Excel. I'm not
even sure that it's possible to do it in Windows - there may be a registry
tweak, but I don't know it.
What you could do is write a macro that does nothing (or something
neglibible - say, display a message that the key combination is not
available) and assign the macro to the Ctrl +C and Ctrl +X combinations. This
will not, however, prevent copying and cutting from the menus, toolbars or
context menus.