Look at the documentation in cua.el:
;; If you really need to perform a command which starts with one of
;; the prefix keys even when the region is active, you have three options:
;; - press the prefix key twice very quickly (within 0.2 seconds),
;; - press the prefix key and the following key within 0.2 seconds), or
;; - use the SHIFT key with the prefix key, i.e. C-X or C-C
;;
;; This behaviour is controlled via the CUA-mode-inhibit-method and
;; CUA-mode-inhibit-delay variables.
There are some other goodies (especially the rectangular support,
started with shift+enter)
So cua.el is worth a look to find out more about cua.el
--
Stefan.