Sina knows nothing.

I'm 5 boxing on an athlon x2 2.2GHz with 3GB of memory and a GeForce 8600GT with absolutely 0 issues. I'm running the 4 background wows in 800x600 with details all set to low (except object distance) and my main window at 1024x768 with some of the sliders up a bit with almost 0 FPS issues, even in orgrimmar I get decent FPS. I have 5 separate wow folders (3 on one HD, 2 on another) which makes a huge difference and I always set my CPU affinity manually which also makes a huge difference.

I also have a 6th wow folder (the main one that I installed originally) that I use whenever I am playing only a single character (like one of my 70s) that has all addons, full graphics settings, etc.

Don't listen to the elitists that say you have to have a top of the line system to 5 box - they're retarded. The fact that people are asking if things like a quad core system with 4GB of memory and a 9800 series graphics card will be enough to 5 box boggles me, since theres tons of posts from people with far less powerful hardware saying they 5 box just fine.