dont forget to back up your default if you want to go back..
first, get the zip here; dont worry its working on GB too..
put the zip file on your phone (or extract it first if you prefer)
open Root Explorer and mount RW(X-Plore file manager also works, you need to set it first to SU + mount RW mode)
rename to Lock.ogg and Unlock.ogg (i think the caps matters so its just for safety)
copy Lock.ogg and Unlock.ogg to system/media/audio/ui
set permissions to this
R W XOwner V V
no need to reboot. enjoy!