Actually you lose your warranty on your video card if it receives any damage from a 3rd party cooling solution, and some manufacturers might void it entirely just for using one (I know for a fact EVGA in particular doesn't totally void the warranty unless the damage is received from the replacement cooler, but I don't know everyone's policies). Plus, Intel's current CPU's have some of the best stock cooling performance of any processors in history. Why do you think there's so much C2D overclocking on stock cooling :P My suggestion would be to plan on spending around $100-150 on a very good case. It makes life easier in more than one way, including component cooling.
Antec, Coolermaster, Thermaltake (there are some others but that's the short list) are the brands I typically research for cases. I recently put together a system with this case from newegg:
Antec Nine Hundred
And while idling with MIRC and Pidgin open and doing anything I need to do that's less system-intensive than Firefox, the CPU cores run so cool that the CPU fan doesn't even need to spin. The case is practically a box fan for my room at this point: if I truly idle the PC (only background OS services running), the case temperature (what programs other than Coretemp usually report) is basically the same as the ambient temperature. Also, Thermaltake's Armor and Tsunami series have come highly recommended to me as well as Antec's P180 series and the Coolermaster Ammo (and FYI apparently the Ammo runs best when you add an exhaust fan to the back).
I've never heard of that Power Supply brand, but if they really believe the PSU needs 3 fans, you really have to second-guess its build quality.
Looking at newegg's page, the reviews are actually quite bad for a PSU; not that you should EVER rely totally on internet reviews, but it's worth looking at. Plus it only promises 70% efficiency, which explains why it needs 3 fans. Most quality PSU's are above 80% the majority of the time, and hit 85% and higher efficiencies. Btw PSU efficiency just means what percentage of its electric current is converted into actual power for your components. The rest is converted to heat. So for example 70% efficiency means 30% of its electricity is being spit out the back of the case as hot air. My personal top-tier PSU's are PC Power & Cooling (typically too expensive/large to even bother, they seem to be oriented toward server style systems more now), Antec, and OCZ. Coolermaster and Thermaltake are basically the 2nd tier there; you generally pay the same amount and get less efficiency out of equivalent products, so not usually worth it unless there's an amazing sale on one.
Here's some quick suggestions for PSUs:
Antec True Power Trio 650W (57A on 12v) - $89.99 after $40.00 Mail-In Rebate
OCZ StealthXStream 600W (72A on 12v) - $77.99 after $12.00 Mail-In Rebate
Basically you only really NEED a system with 35ish available @ 12v, with a Quad and an 8800GTX . These are actually both massive overkill (but if your components don't draw max power capacity from the PSU, it's not a problem at all) for your system, but due to the transition period of PSUs right now, the market is a bit odd. You can often get higher efficiency, more stable, quieter power supplies that are
more than you need for less money than ones that support
less power. I won't get into why that is though... that's a whole other thread.
As far as motherboards go, unless you plan on going with an SLI dual video card setup in the future (which I personally wouldn't recommend), you can find a motherboard for half the price I'd bet. The Intel P35 chipset is just as good as the 680i (and in truth has had none of the issues the 680i has, although they seem to be getting worked out). Here's the motherboard I decided on; note that I picked it based on supporting the memory I wanted, and being cheap. I won't be upgrading to SLI so I only need 1 PCIE slot, which saves $$ over SLI mobos.
Gigabyte's P35-DS3R. They also have a "P35C" model which is identical but has a different onboard audio processor and supports DDR3 memory (but if you're buying 4 gigs of DDR2 righ tnow, I don't think you'll be upgrading to DDR3 any time soon). I believe Asus also has a similar and competing motherboard but I think it only supports DDR2-1066 and above from what I remember, so not really applicable here.
RAM is pretty difficult to put a finger on since the models/ICCs/prices change so quickly. My general experience has been that Kingston/Crucial/OCZ are the most reliable, with Corsair and some others along the 2nd tier there. Just my opinion though (based on actual experiences however). The problem with finding RAM deals is that if you buy 2 sets of 2x1gb sticks, you can only redeem 1 of the mail-in rebates if they are there. To be honest, I consider this to be the best deal in DDR2-800 right now; I bought this exact pair for $15 more and thought it was the best deal back then:
Crucial Ballistix DDR2-800 2x1gb pair.
You could grab a pair of those and just send in 1 rebate I guess. Feels like losing money to me though. Maybe you could find a friend to order it and get it shipped there, etc, and then just give them the money for the transaction (rebates are 1 per product model per household). But even then it's a better buy than the Corsair TwinX.
Honestly until you get into CAS3 DDR2-800 or DDR2-1066 and you're paying closer to $150-200 per dual-channel set, performance increase vs cost increase isn't all that impressive. There's some OCZ Reaper that is in a competitive performance and price position as that Ballistix that you might look into as well, with similar latencies.
And for the most subjective part: the CPU. Basically for your price point you're deciding between a slower-clocked Quad core vs a higher-clocked, higher-FSB Duo (the 6850 specifically). Personally for gaming I'd recommend the faster dual core, since there are really very few (if any?) games even USING 4 cores, let alone putting emphasis on utilizing them well. Unless you're doing on-line video editing (audio editing doesn't even really need a quad), or graphics design of some sort (and for modders: U3 engine's editor will utilize 4 cores apparently), you're simply not going to be using half of your CPU most of the time. In my opinion buying a quad core for gaming is about akin to buying a physX card right now... although to be fair there's a much higher chance that multicores will be utilized
further down the road. My (somewhat controversial) thoughts: by the time quad cores are really utilized, I'll be upgrading my PC again anyways, so why would I need one now?
As far as compatibility goes, as long as the Case, Mobo, and PSU are ATX form factor (PSU will actually be like "ATX12v2" or something most likely), the vid card is PCIE16x and the mobo has at least 1 PCIE16x slot, and the hard drives are compatible with the mobo (i.e. you don't want 3 IDE hard drives if your mobo only has 1 IDE port but 8 SATA ones, you want SATA drives), the only real things to worry about are CPU and RAM. Most mobos you'd even be considering are specifically designed for Core2's, so it's just a matter of matching up the CPU front side bus (FSB) that you decide upon and making sure the mobo supports it, and then doing the same with the memory speed (800 vs 1066 for example). Most mobos will be clearly marked for these, however, so it should be fairly straightforward.