Please keep in mind, if you are going to be playing games, one of the most important pieces is the Video card. Now, the Best Buy branded box has a Geforce 2....What type of Geforce 2? There are about a dozen versions of the GF2 ranging from bottom feeders to top of the line. Also keep in mind that GF2 is technology from a few years ago...an eternity in the PC business. The newest graphics chips are based up on the GeForce 4 (by Nvidia) and Radeon 8500 (by ATI).
I find the best thing to do is BUILD YOUR OWN COMPUTER. I priced out a system better than the one you listed below for around $500 in parts + monitor. It might seem like a hard task, but it is very simple especially with the Internet as your resource. Besides, the knowledge you would gain would be immeasurable and I am sure some of the PC Gurus on this site would be more than willing to help in times of trouble
My .02
