Agreed, if you aren't running 1900x1200 or above SLI isn't worth the money. If you run 1680x1050 like a normal person a single 4870 will play anything you want.
Also:
Vista is a RAM hog for a reason. It preloads programs into RAM, so they appear faster when you want them too. I seriously cannot see how this is a bad thing unless you do major CAD, music, or photoshopping and you need the RAM.
Also also, WTF does it matter if your RAM is being used? What else is it there for, if not to be used? Otherwise its just taking up space and electricity for no reason.