Whoa, slow down here. You're overcomplicating things.

First, the FSB is used to determine how quickly the CPU will be able to talk to components, and yes it is governed by the CPU that is plugged in. To determine the FSB, look up the CPU that you want to buy, then find the details for it on the manufacturer's web site.

For example, I recently purchased an AMD64 X2 4200+ processor (dual-core). According to AMD's web site, the processor runs at an actual speed of 2.2 GHz, and as an FSB (system bus) rating of 2 GHz.

You don't really need to worry about the FSB, as there isn't any control you have over it. Instead, decide how fast of a processor you want (or can afford), and go from there. Worry only about what you can control.

The kind of memory you need is also based on the CPU you select. Basically everything surrounds the CPU you decide to go with, as the CPU is also the powerhouse of the entire system. Most processors available on the market today will take DDR2 memory. The newest processors may lean toward DDR3. I suggest getting the highest memory speed your CPUt.

Start with your processor. Then select a motherboard that will support that processor. That mainboard will most likely have onboard LAN and sound as well as a good supply of USB ports. Select your memory next, going with the kind of memory that the CPU can support. Beyond this you will need a power supply and video card, as well as a case, keyboard, mouse, and monitor.

Hope this helps. Let me know if you have any further questions.

I don't overclock any of my computers. I've heard of people frying their motherboards and processors (literally) from overclocking, so I don't even think of trying it.

And I was actually mistaken in my previous post as I mistook the "bus speed" for the "FSB speed", which are different concepts.

Multipliers are still calculated the same as before: FSB * multiplier = core speed. The web site techPowerUp! has a CPU database that lists many of the modern processors and provides technical details on them such as FSB and the multiplier. I also read somewhere that some processors are unlocked as far as the multiplier is concerned, mainly Intels if I remember correctly.

The speed of the memory does make a difference in the actual performance of the computer. However in your comparison, DDR2-800 vs DDR-400, the former is still faster. It can do up to 800 million transfers per second for a theoretical bandwidth of 6.4 GB/s. DDR-400 is half that: 400 million transfers per second with a theoretical bandwidth of 3.2 MB/s.

However if you were to compare DDR-400 with DDR2-400, then things get interesting. Both have the same transfer capacity and theoretical bandwidth, but the former has the potential to be faster because it has a higher memory clock, 200 MHz vs 100 MHz. Theoretically DDR2 is supposed to see performance gains over DDR, meaning that DDR2-400 is supposed to outperform DDR-400, but this was not always the case depending on the particular memory brand being used.

Now which memory you require is still going to be dependent upon your motherboard. Whatever your mainboard requires is what you're going to be using. Most mainboards today will require either DDR2 or DDR3, with DDR3 right now being exclusive to mainboards for Intel processors. DDR3 memory is also faster than DDR2.

One other thing you may want to take into consideration is the video card to select, but this also depends on what you're planning to do. If you're going to be doing any kind of gaming, make sure to select a faster video card as well, as the video card will also make a difference in performance -- i.e. the faster the video card, the less the CPU will have to wait for it.

I hope I've assisted you, but if you feel you need further assistance, let me know.

I don't know where you heard that using 4 sticks drops the memory speed, because it's my understanding that that isn't close to true. All should still run at their full speed.

I'm also using Corsair memory in my computer, which I've heard is a good choice. Crucial is supposed to be better, but they're much more expensive as well, so Corsair is a good choice, and what you've picked is what I'm using, actually.

For better performance, I would recommend finding a motherboard that supports HyperTransport since you're going with an AMD processor. I think that nVidia chipset mainboards are the only ones that support it, though, but look around. I'll also assume you're going with the retail AMD processor that comes with a cooling solution already and the nice 3-year warranty.

Otherwise everything else looks pretty good. Nice choice on the power supply, too. Also make sure you buy some more fans for that case. It comes with two already, according to the listing, but consider buying more if the case has places for them.