Scriptable Mask?

Hi! Alright, there’s a few ideas from this one site ive been asking about here.

Ive seen this transition on other sites as well, and so my question is, is the way the backgrounds come in, after they load when you click a button, some sort of scriptable mask? I checked out the scriptable mask tutorial here but it didnt seem to be about something like that or am i wrong?

Also another question about backgrounds - ive got backgrounds set, but every time i click on a button, there’s like this split second lag time, almost like the screen blinks and then loads the background. What im talking about, again in the above example, the original background can be reloaded when clicking on the news button, but if that background is already loaded, there’s no indication that its being ‘reloaded’ by clicking on that news button; but in my swf right now, doing the same thing, it obviously shows its reloading the background in mine - any ideas on how to get that not to happen? Im sure its a movieload actionscript ref. that i dont know, but im not sure! Any ideas would be greatly appreciated on either of these, thanks!