Everyone so far is dead on regarding the power supply. Simply put - 350 aint gonna push what your running well - and you havent even mentioned how many other devices are gonna draw power (those hard drives and dvd burners require juice too!) A 450 watt will run most single HD & DVD rigs with a single vid card that does not require a power plug for itself. The older AGP cards required a plug direct from power - but since it looks like your moving to PCIe - that frees up some demand since PCIe cards USUALLY (but not always) are powered only from the slot. If your running multiple HD's or DVD readers/writers - or are going to do a dual card setup at some point - you will want 500 watts or more.
As for the question of the Quadcore processors... its smart to go with a mainboard that will support it, but I wouldnt suggest ponying up the cash for the processor yet. At this point - there arent any games or apps that take advantage of it (rare for a game to even really use dual-cores properly).
Since we are on processors - do some research on Intel vs AMD performance against price. When Intel released the 2nd generation of dual cores, they really trounced AMD performance wise - but AMD has stepped back up with the am2 line. If your wanting to go Quadcore later though - Intel has to be your choice now because AMD's entry into that "market" is still vaporware. However realize that going quadcore means a Xeon chip right now. Xeons are their own little world mate.....
Ram - definitely go 2 gigs to start. All games are memory hogs - and I can tell ya - running SH4 on my new rig with 1 vs 2 gigs of ram makes a VERY large difference. Just go with what your gonna want anyway.
Vid cards are really a personal choice. I am going to say something that every Nvidia AND Ati fan out there are going to get upset over - but its the truth. The two brands are about the same when you take equally spec'd cards. Ati tends to give slightly higher frame rates - but the quality doesnt always match up - though it is close. The real decider for which brand you want is going to be your chip choice. AMD owns ATI - and Intel has partnered with Nvidia. If you go with a AMD chip - they tend to run a little happier with ATI GPU's - same goes for Nvidia and Intel. The difference isnt large - but in gaming systems every little bit helps. Whichever you choose - go with the largest card you can afford, spec wise. I honestly cannot support going dual GPU's - the increase you get isnt really that great for the cost - and its actually a big pain in the rump for most to get it to work right. The folks I know who have it - use it mainly for multimonitor (4 usually) support rather than frame rate increases.
Also you may occasionally here that you dont need more than 256 on a card. That was true in the heyday of AGP - but the standard has changed. However, dont go above 512 on a card (they are available with higher amounts) but the return in performance is negligable, but you'll bleed for a card running that higher number. Also pay attention to the specs - if its says "SE" (for Special Edition) or something - check the numbers - alot of cards are sold as budget highends - but have the speeds limited. No use paying for something then finding fine print.
A couple of other suggestions - if you havent already - swap your drives to sata - the increased transfer rate really makes a difference with newer rigs. IDE drives are still supported and work great as always - but the additional throughput rocks when it comes to load times. May or may not apply to you - but its often missed and becomes a bottleneck when people use their old drives in new machines. The second is when you build the box - most mb's come with everything (including vid) integrated. ALWAYS remember to turn the video shared memory OFF (set to none) or else the mb will apeture graphics memory but it wont be used.
Cooling is again a personal issue. My take on it - if your not overclocking - just go stock with a couple of case fans and good filters. A slot fan close to your GPU for additional airflow is also a good idea. Keep the filters cleaned, the PSU and box blown out occasionally - and you will be fine. However, if your gonna overclock - then yes - get a true copper heatsink with a whirlwind fan (there are a number of good makers out there), or if your really wanting to go big - look at liquid cooling. That however can be bloody expensive.
I notice you didnt include a sound card on your list. That might be a smart move - while the X-FI boards from SB are great - they seem to not like some rigs or some games. Actually that could be said for ALOT of SB boards.... I have an SB board in my rig - but its disabled except for the gameport. Onboard sound (AC'97 based mostly) has come along way in the last few years.
You also didnt include a physics card. Granted I don't know your budget, but if your really going to go all out on a gaming rig, you will be glad you invested in one. While not all games support it intentionally - properly installed the CPU will push most physics calculations to the card - making for a huge difference at times. An example would be when someone hits a ship with a high powered torp in SH4 (or hits a ammo bunker) and sets off a chain reaction of explosions. All the pieces flying off often cause a small stutter in FPS - with a physics card - there is none of that. As games get more realistic - the need for this addin will become more and more visible.
Either way - enjoy mate!
