IMO it double the memory (and its nto a value RAM either)
It's the RAM I use, and the same type of graphics card. Running under even Vista with that RAM and that card I get 0 problems with intense games. 4GB is nice, but it's not required for what he's wanting to do with the system. If he has the extra cash then he could get the extra RAM, but otherwise I wouldn't bother.
afast HDD with more space, a brilliant CPU cooler for the price, the PSU that is still over kill, and CPU that will clock to about 3.6 if not more, a PROVEN OCing mobo
He might not even be overclocking therefore the cooler would just be a bonus, even if he was overclocking midly the stock cooler would be sufficient. 450W isn't an overkill, it's borderline, it's more of a PSU that you should be using for a lower end system not a mid-high end system. 650w Corsair would last him through this PC and his next PC.
Those are my opinions anyway.
Thinking about this, or would I be better with just two gigs of RAM, a smaller hdd, and a slightly better GFX card?
I would switch the hard drive for a
Samsung F1 500gb as it's only about £2 more. It really depends how much hard drive space you want, if 250GB isn't enough then I would stick with the 500GB model, otherwise I'd just go back to the 250GB Deskstar if that's enough for you

Also depending on what resolution you game at, I would stick with the 4850 you have in your spec you put in the picture. If you are gaming at resolution around 1080p or higher then I would suggest looking at the 4870 for the extra power. The 4GB RAM is not really necessary, but if you can stretch a little bit extra it's worth it as RAM isn't that costly.