I have seen a comment on another forum (I can't remember exactly where) that says that screensavers stored in System32 and winsxs (64 bit systems only), and one other folder (I don't remember which) always show up in the list in the dialogue box for choosing a screensaver. However, in 64 bit systems, they are (often, if not always, not in winsxs itself but rather a subdirectory of winsxs). It is always a safe bet to put any screensaver you want to use in System32 and that is what I recommend.