well, the new wolfdale 8400 that he put in that build would be better for gaming for a few reasons.
first off, No games out there at this moment work using 4 cores, however multiple games are optimized to use two cores. therefore your q6600 can only utilize 2 of its cores at 2.4ghz for a game, whereas the 8400 can utilize both of its cores at 3.0ghz. notice that 3.0 is higher than 2.4
both cpu's will overclock very well, but with the newer 45nm technology in the wolfdale e8400, you'll reach higher speeds much easier.
i think you would be better off with gurusan's build.
as far as the different brands of the video cards go... they are all the same components except for a few minor things that dont make much difference hardware wise. The real difference lies in the customer service, and the special benefits you get. forinstance evga has a step up program. this allows users to upgrade their video cards within 90 days of purchase to a newer card, all they have to do is pay the difference and send em their card and they will get the newer card... this is great for people that are unsure of what they want, or people that devote their lives to having the newest baddest cards on the market... now ive heard some criticism from people on the speed of their upgrades, but i myself have never done it so i cant offer any first hand knowledge. i guess before i start typing a ton and make this really long winded... they are all pretty much the same, dont worry. they all have their own personal versions of factory overclocked settings that will cost you 10-40 bucks more, but its not really a huge difference, i dont think you'll be able to notice it without benchmarks, and you can always overclock it yourself.
as for the ram, im not sure why gurusan picked that instead of a 2gb kit of ddr2 800. and yes accendo, 800 is faster than 667... he may plan on you overclocking it... im not sure, but im weary of going against it, b/c he knows what he is talking about... wait for his reply.