The rig on FiringSquad is a bit outdated. I helped a friend build a rig not so long ago from scratch (mouse, dvd drive etc... included in the price) with the combo prices and mail in rebates from newegg it cost him under $1100 tax & shipping included, but what he got is a ATI HD4850, with E8400 core2duo and a samsung 22" screen, antec case & power supply etc... all the other parts were of very high quality. I don't think a laptop can ever beat that, maybe the $3000 one with 2 graphic cards can, but I doubt it. If you allready have some components from an older computer and take less quality parts, it can go much much cheaper and still be an awesome gaming rig.
I myself had the first eeepc and it is a joy to use but sold it cause of the small screen. I am planning to buy a netbook again this summer after the competition becomes available in a few weeks (wind, acer one ...) supposedly they will cost less than $350 and better than the eeepc.
As chuwy said the gateway is the definite choice if you go laptop but compared to a similar priced desktop like the system mentioned above, it is several leagues apart.