[Tristan Lall]

So, what's the budget? Also, do you plan any overclocking?

You look like you're on the right track for the most part, but I'd question the choice of processor. The Q6600 has a good price-to-performance ratio, but it's getting old, and is about to be retired by Intel. If you want four cores—note that you don't necessarily need them—you should consider a Q8300 instead (it will cost about $40 more than a Q6600, and should be available any time now), or even a Q9300 (for a bit more money). These have larger instruction sets (mainly, they add SSE4.1, which could come in handy, and drop VT, which is no detriment to you), are more energy-efficient (fundamentally because of their smaller transistor size), and are faster (both in clock speed and FSB speed). If you'd be satisfied with two cores, you could also use an E8500 or E8600 (which have much higher clock speeds), and are priced comparably to the Q6600 and Q8300.*

The cooler will be fine, but then again, retail Intel processors come with good enough heatsinks (OEM ones don't). Unless you're overclocking significantly, or want to have a quieter fan, there's no need for an aftermarket heatsink. (For non-Intel heatsinks, verify the component clearance between the heatsink and the motherboard. This is usually described on the heatsink manufacturer's website.)

The hard drive is probably fine, but you might want to consider moving up to one of the 640 GB versions (it's got higher data density than the 500 GB drive, but also uses two platters—as a result, it will be a little bit faster). It won't cost much more. Good move going with the Caviar Black—the extra warranty period is worth the increased cost (however, the extra cache is useless).

If you've got another system on the same LAN, then you don't strictly need the ability to write CDs/DVDs; you could pass files over the network to burn them remotely. But it it were me, I'd spend $30 or so on a DVD burner. Although most in that price range are pretty much equivalent, you should shop around to find one that supports all major formats (some omit DVD-RAM, in particular).

I wouldn't bother with the sound card—your motherboard has integrated audio, and you've only selected a 2.1 channel speaker system anyway.

With the price of DDR2 RAM what it is (very low), you might want to think about another 2 GB (or 4, if you'd like). 4 GB of RAM will be just fine for now, but if you're planning to keep this computer for a while, you'll probably appreciate having 6 to 8 GB in three or four years. If it's out of the budget, don't worry about it. Your RAM could stand to be faster if you're planning on overclocking, but this won't make too much difference (your motherboard will apply an appropriate FSB-RAM speed divider anyway).

The case, video card and motherboard all appear to be solid choices. (Given the good price of the Radeon 4830, you could easily add another one in Crossfire at a later date, if performance was insufficient. It will run at PCIe 8x, but that will be fine.)

*When multiple applications (or more precisely, threads) are running, and have lots to do independently of each other, the quads will be significantly faster. At this point, though, most games and many CAD programs don't do much to assign tasks to multiple threads. This means you'll get better performance, but it won't often be twice the performance of a dual. (For technical reasons related to the processor technology, it's easier for Intel to add cores than to add single-threaded performance.)