Looks like a nice rig. One wonders, "If it is already built, why ask for advice?".
Except for long renders of Video codecs (transcoding) and effects, your build would handle almost anything else that I do. I would call it "a very thick client" , Like a supercharged ATOM/ION, on streoids. Shouldn't drag, at all, as long as you don't have extreme gaming or HD video expectations/aspirations.
when i play games, say CoD 4: MW2, Resident Evil 5, or any new games, when i turn on AA, my game lags, or say my Frames-per-second decreases, so i usually remove the AA settings... what can i do to solve that problem? do i need to buy a new GPU?
Others will have to answer that. Games are not high on my list. My big plan (only just lately) might be to get a PS2 (used) so I can play all those good ol' games for cheap (and still be running other stuff (music, etc.) on my computer) It's all running thru a mixer ... works.