What makes AMD good? AMD uses a different archetecture than Intel, meaning a processor with say 2ghz (the 3200) can easily beat Intel at gaming due to AMD having shorter skinnier pipelines meaning it can do more instructions per clock. AMD has also done away with the slow front side bus, and replaced it with hypertransport which is on the cpu (the memory controller is on the CPU as well) where as the FSB is on the motherboard. The memory controller being on the CPU also means that dual channel ram has alot more bandwidth, 6.4gb/s rather than having 3.2gb/s when being in single channel.
DFI lanparty are good because the amount of overclocking options in the BIOS, which means you can get a higher overclock, and alot more stable overclocks. They are also a very stable board, and not too expensive.
Nvidia supports something called pixel shader model 3 on their 6 series cards, which is the main reason for choosing their cards. PSM3 will be used in the next games due to being alot more efficient than PSM2 which ATI went too early on, and the game developers didn't use it. With a ATI card, you would have to run a PSM3 game in direct X 8, which does not support PSM3, and so you will not be getting your money's worth of eye candy.
The OCZ platinum rev. 2 are great overclocking ram, which use Samsung TCCD, but now use Samsung TCC5 for the intergrated circuits. They use Brainpower printed circuit boards, which are the best avaliable. The TCC5's can be good, but there are some that are not so good pick out of the bunch. If you have the money, than G. Skill uses TCCD's and brainpower CB.
Seagate and western digital have been known as the best two, and it is what ever you prefer really. They are both extremly reliable, fast and quiet. Although W.D. is known to be more reliable, and seagate has been more quiet. But they are still both as good as each other. (I chose seagate.) Sata is a better interface than the conventional IDE - which uses big cables, which effect air flow. Although IDE has lower bandwidth than SATA, hdd do not use it all. They use about 75mb/s (IDE has 133mb/s max, and SATA has 150 SATAII has 300) SATA has the advantage with the interface, meaning it can pull ahead there. Also, when putting 2hdd in RAID on IDE, you have to put it on the same cable, which means that it has to share the bandwidth, and only one hdd can operate at one time, which is bad. With SATA, they have their own cable, with dedicated bandwidth, and they can work at the same time.
The PSU is very important, and you do not want to put a cheap one in your PC, as if it goes, it can take out your hardware with a voltage spike. When they go, it fill also give you a fright, as there will be a blinding flash, and pouring out alot of smoke. Cheap PSU's do not give out their rated wattage, or AMP's on the lines, meaning it will effect stability, and the performance of the parts. The voltages will not stay at the required volts for the line. E.g. the 12v will fluctuate to dangerously below that or above that. A good PSU will be very reliable, so will not die on you. When it does die, it is more likley to just die a quiet death, and not take out your PC. The AMPS will be nice and high. The wattage is done in a real life enviroment, where it is at a room temperature, and is an average and not a peak. The fluctuation will be kept at a minimal.