Ok, you don't need to be a comp wizard to learn how to upgrade your video card/ram. Those two things are the easiest things to upgrade. Btw add 80 bucks for some random dual channel ram and your set. 990 for a great gaming pc that will run bf2 and much more.
It really depends. Custom builds are better cause you can use a high-end motherboard and they are upgradable. You can choose your stuff. You can't choose with Dell. But on the other hadn, if you don't want to build your own, Dell's are easier to install. There are also many companies that build computers where u can choose the parts.