by extended desktop...you mean dual monitors? The evga has two ports but one is dvi and the other is vga.
But to have extended desktop.....you need another monitor. I would stick with the build i suggested and when you get like $350 later down the road, you could get another stick of ram and another monitor.
Butif your going to use dvi (dvi is the best since it does all the fitting on the screen for ya
) you might want to get a video card with dual dvi ports.
You can either stick with the evga 7600gt i suggested, or if you want the dual div slots then get the xfx 7600gt
You can dual monitor with the evga but having a dvi and a vga is kinda weird cause one auto adjusts for you and the other you have to play around with. I don't know about you but that would get on my nerves, having one monitor prefectly aligned and the other always off by a little but thats just me
In the end its your choice, but you do need two monitors to have a extended desktop.
And this setup would be able to run WoW and CS:S on high settings easy
edit: and yes this is everything you need to emerse yourself in the digital world