Preface - opinions about hardware are a dime a dozen. There are 1000's of components you can build PCs out of, so there are ridiculous numbers of potential combinations, and almost an equal amount of information and opinions related to them. When I'm about to build myself a new PC I do a ton of forum reading, review reading, hardware site scouring, etc to try to get a composite view of the present and near future states of hardware and I *hope* to make good buying decisions. I love PCs and PC gaming, but sometimes the volume of hardware involved is overwhelming!
For some components, like getting a hot video card, the choices are fewer and easier - but when it comes to cases, memory, motherboards, CPU options, and all the rest of the components, there's a lot more flexibility and related debate.
You might want to try a question like this on the anandtech forums or tom's hardware forums where you'll get way better replies - maybe too many and too much (most hardcore tech weenies have preferences for every little component). They would also recommend you build your own PC...so...eh...well...try at your own risk! But a lot of people do post "potential build" threads for evaluation.
It's also good to indicate what you use the PC for - pure gaming? Work? What type of work (PC intensive like CAD, graphics, programming, etc or just business stuff with productivity apps that'd run on anything, etc). A mix? Most people will want to suggest parts/builds based on how you use your PC, as it's often a critical factor. A grandma that just surfs the web and doodles in MS Office doesn't need the same PC as an artist doing poster layouts in Photoshop or a hardcore gamer.
And it's good to know what your budget is like (although apparently, based on the parts you list, money is not a problem - it looks like you went to Alienware or something similar and picked all the most expensive options possible).
-Should I get XP or Vista and wait out the issues?
Tough call - kinda depends on what you use your system for and what you want out of it. Personally I'd get XP (Pro for me) w/ an upgrade to Vista option if you still can. XP is rock solid and great for gaming. Vista still has issues with drivers, issues with 64 bit, and there aren't that many games coming out that will be DirectX 10 only (DirectX 10 is Vista only in a stroke of anti-genius) - and all of this will probably persist for quite a while.
For absolute stability and less hassles, go XP now with an option on Vista later. If you want all the graphical bells and whistles of Aero Glass and/or like dealing with driver misery, incompatabilities, and troubleshooting problems stemming from your OS, then go with Vista.
IMO, if you like to play a lot of PC games and even if you use a lot of pre-Vista PC software, you probably should stay away from Vista if you aren't up to doing a potentially large amount of self software support.
-Should I go for duo or quad core processors?
I don't think much software today is even fully leveraging dual core, so I'd think quad core is even more overkill. I'd imagine the days of seeing "requires a dual core processor" are still a few years away. But since either are common and Intels are nicely priced these days - I'd go with whatever floats your boat. It certainly can't hurt to have dual/quad core (I have dual) and some day more software will leverage it.
-What motherboard should I get and will support duo and/or quoad processors?
Tons of options here and you'd be best served at a more techie oriented forum. The one you listed looks like an overkill monstrosity and is probabaly expensive as hell. You could probably get something similar but less over the top and be well served. Generally the only people who will use 100% of an over the top board are hardware enthusiasts. You probably don't overclock (or you wouldn't be asking these questions) so you don't need that capacity in a board. You just need something that supports the features you want, like SLI, a good chipset, matches your CPU, has enough slots for whatever you want to plug in, supports the number and type of hard drives you're using, etc. If you're working with a vendor to build your PC, the boards they list should be compatable with the CPU and options you want - otherwise they'll let you know.
-Do I need a network card?
Almost all motherboards (like the Asus you listed) have built-in gigabyte network capacity, so you don't really need a network card. I suppose you might get higher performance out of one if you really know what you're doing but for 99.99% of humanity, the onboard ether will handle anything you'll ever do. I would say, no, you don't need a network card.
-Do I need a voltage regulator?
Not a bad idea for a high-end computer with a 1000w PSU and components (video card) that draw huge amounts of power. Consistent power is a good thing. The one listed in your post is probably 100x beyond overkill and insanely expensive.
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Some of the parts you list are overkill or unnecessary. It kind of looks like you picked all of the most expensive parts at a prefab site like Alienware, and I shudder to think of what the final cost would've been that they listed. It's so much better to build your PC yourself - you get high quality parts, know exactly what you have, and pay significantly less. Anyways, apparently money isn't an issue here, but you can avoid simply flushing some of it if you want to.
You might check out some reviews of the 8800 Ultra from anandtech and other similar sites. The Ultra only outperforms a GTX by a fraction and many say it's a waste of money. I'd say just get a GTX and if you need more oomph in a few years upgrade the card (often an easy way to get more life out of a PC unless you're hurting for RAM, which you won't be) or go SLI with another GTX (and make sure you have insane cooling
). Supposedly the next generation of NVidia cards will be out for the holidays.
I wouldn't get a fire wire card - many motherboards might already have it built-in (pretty sure the Asus you listed has it) and I'm pretty sure it's an out-of-date or seldom-used technology anyways. Unless you have a firewire device you need to hook up, I wouldn't even have it at all.
No real need to get a new mouse or keyboard unless you don't like what you have now.
You don't really need an over-the-top cooling system unless you're an enthusiast that'll be overclocking and such - but it can't hurt. It's definitely a good idea to have adequate cooling with a beefy PSU/Video card combo. If you're not building yourself and don't know about case fans and adequate cooling - just go with the (recommended?) beyond overkill solution.
I'm not getting why the suggested case has a built-in PSU that's going to be replaced.
I'm a big fan of Corsair (XMS) memory so that's a great choice (keeping in mind that most people have their preferences). 4GB is probably overkill now since 2GB is a very healthy amount these days, but 4GB is a great choice for making the PC last several years.
I personally wouldn't go overboard with a sound card but it really depends on how you use sound and whether you're an audiophile or not. I love music (I'm a musician and have an obscene amount of CDs and such) but I'm not really an audiophile. On my PC I mostly use headphones and my desk/pc setup would never support a 5/7 speaker surround sound setup. I use an inexpensive Creative card just to get sound processing off of my motherboard/CPU. I wouldn't really go with a high priced card unless you KNOW you'll use its full potential - why pay for something you don't need and won't notice? Most motherboards have high quality built-in onboard sound these days, or you can go with an inexpensive card for (pretty much negligible) performance gains).
Round cables are an excellent idea - they're nice for better airflow and cable management in your case.
eVGA is a good brand for video cards, IMO.
I don't know squat about the case you've listed - but there are a few considerations. You pretty much want to make sure it has some front USB ports, so it's easy to plug in your iPUD/MP3 player or other USB devices you want to be able to easily deal with. You might want front audio capacity depending on how you use your PC audio. Steel and aluminum cases are generally cooler and quieter.
