pretty nice, I know myself how tricky getting splitscreen to work in flash, and it means things do run extra slow as its pretty much drawing everything twice. also you might not know but lines are very slow for flash to redraw, in most cases using fills instead is actually faster and less laggy, unless of course you are drawing all of the level at runtime, in which case a few more adjustments may be needed.
if you want I might be able to pull up a .fla of a splitscreen deathmatch game I made a while back if you want a nosey inside, the code is prolly pretty messy/lazy but it worked pretty fast
anyway, you get a because even managing something like this takes a headache
not exactly, i have two movieClips using scrollRect and each object has an object assigned to it with its x and y position, then there is a scroll value of the player position in each MC and i have a function so everyframe it updates all the object positions according to the mc's object x and y with the scroll amount
So as i said there are two moveclips. I thin kthere is better way to do it. Tough you will nedd to use bitmapData. You can have one mc and two bitmapData. On each bitmap data will be drawn from a source movieclip with players offset. In such way you will have 2 times less objects(moveclips)