ok, theres a lot of changes you should make to the spec in the pic, here is my suggestion:
The 4870 is better than nvidia's equivalent in its price range: the GTX 260 and much better than a 9800GT. like pasty muncher said above, you can not have 2 Nvidia cards in SLI on an intel chipset motherboard(p35,p45,x38,x48) but you would need an Nvidia chipset (650,690,750,790 etc) but Nvidia chipsets are not as good as Intel chipsets for stability and overclocking.. and are more expensive. I chose the 1Gb version of the 4870 rather than 512mb as its only a couple of pounds dearer and will help your mate especially if he has a high res monitor.
The p45 ASUS motherboard is a very popular board, stable and good for overclocking, considerably better than the p35 in your pictured spec.
i chose a 640gb hard drive as 320gb or 640gb hard drives have denser platters and are therefore faster than 250/500/750 gb hard drives.
If your mate is using the pc primarily for gaming and not video encoding etc then a dual core is better than a quad core as games are not optimised for 4 cores at the moment, and won't be for a while. It's better to get a higher clocked dual core which overclocks really well such as the E8400 which should get to 4Ghz very easily with the p45 motherboard i recommended and the CPU cooler that i will come onto..
The antec 300 is a really good gaming case with lots of helpful features such as dust filters and a cable management section at the back... it also comes with 2 pre-installed fans with speed switches. Its still good for the price at overclockers but can be bought for about 12 pounds cheaper if you look elsewhere. It doesn't have frontal intake fans but has slots for them which is why i added in 2 Xilence fans which will definitely improve airflow from the front to the back of the case. This case is by far the best one in its price range, you wont find many people that would go for another case..
The Hiper Power supply you have in your spec isn't a very good choice, they are renowned for blowing up. i made the mistake of getting a cheap power supply when i bought my pc a few months ago and it didnt have the connectors i needed for my graphics card and some cables weren't long enough, so i ended up buying another one. The corsair 520 (the one i got) is easily powerful enough for the spec i made and is modular, meaning you have individual wires you plug in and use only the ones you need, improving cable management. if you would like some more juice then you can get a Corsair 650Watt for the same price but it isn't modular, id recommend this for if your mate is considering adding another 4870 in the future.
The noctua CPU cooler is just as good for cooling your CPU as all the other premium ones, but is much quieter, noctua being renowned for their quiet fans whilst still peforming well.
the 8000 ram you chose is a good choice as regular 6400 ram can struggle a bit if your clocking up to 4ghz on your CPU if you want 1:1 RAM/FSB timings which is helpful.
hope iv helped, if you have got any questions then just post here
