Putting together computer for running two acocunts - looking for some input!

Yay another of these threads. I've read around a bunch but would like to get some input before going through with everything. Long post with my current computer and WoW situation to show you were I stand.

I run two accounts on one computer and one 24" monitor. I don't split screen and I don't use AHK or Keyclone, just good old alt-tab. So yeah, not the most efficient set up in the world, but it works for me, and I likely will get into using software keystroke sending at some point now that it's more widely accepted by Blizzard. As much as splitting my windows would allow me to see what's going on with both screens, I like to abuse my full 24 inches of monitor space and also find myself... tired (eyes, headaches) by all the movement going on in the other screen, which I suppose is funny considering the jarring nature of alt-tab, but anyways! And of course always Firefox and 4-10 tabs open in the background.

Also of note, I live in Hawaii and I am not able to get AC in my room, so cooling can potentially be an issue, not to mention dust. In addition, I'd like my computer to be quiet if at all possible.

My current system is about three years old and wasn't top-of-the-line then. It currently has in it:
Pentium D 820 Dual Core - 2.8 GHz
2 x 1GB RAM - not sure exact stats on those
74GB WD 10k SATA 1.5GB/s Raptor drive
160GB 7200 SATA 1.5GB/s drive
Windows XP Home
Nvidia 7800GT 256MB - not positive on these stats, borrowing friends, but believe it's the same as the card I had previously.

I run one instance of WoW from the Raptor, and one instance from the slower 160GB (which also has the operating system on it...). My settings are 1920x1280 with I believe 32 bit 1x AA for both and have both running in maximized windowed mode. Settings are mostly low except for how far I can see into the distance and usually spell effects are medium to high. I generally am running okay at 20-30 fps while two-boxing solo/single group content. Not great, but more than playable. However in cities and some other areas frame rates can drop below 10 fps, making things quite difficult or frustrating. A possibly fps related issue is I always have to lead with my priest and my paladin following with crusader aura. If the paladin leads, the priest inevitably falls behind enough to lose crusader aura and then it's game over for follow. However, as my paladin is the one with a gathering profession, I'd prefer to lead.

Taking that all into account, I'd like to upgrade my computer to the point where I can play two accounts and can't much tell the difference from playing one - quick loading, 40-60 fps, 25+ in densely populated areas. I'd hope this computer will be able to continue doing that in the upcoming expansion and basically last me for at least 2 more years with minimal upgrades and without breaking my meager budget of about $900 + $100 for shipping to Hawaii. I've built my own computers a couple times before, but my last computer was a Dell and it's been 5 years since making my own so I've been trying to read up on specs, bus speeds, HD interfaces etc. but it's a bit overwhelming!

Antec Sonata Plus 550 Black/ Silver Steel ATX Mid Tower Computer Case 550W Power Supply - $110
Seems like this should be a simple but sufficient enough case to buy.

ASUS P5K-E/WIFI-AP LGA 775 Intel P35 ATX Intel Motherboard - $150
Seems solid!

Seagate Barracuda 7200.11 ST3500320AS 500GB 7200 RPM 32MB Cache SATA 3.0Gb/s Hard Drive - $80
Can't afford the new 3.0Gb/s Raptor, as seems to have only one $300 flavor. I don't know how much that matters anyways, so just getting a moderately sized new drive, and then see how it compares with my older 1.5 Gb/s Raptor. I honestly don't know despite my reading here whether a harddrive for each instance of WoW is better, worse, or negligible.

Now the parts that I'm not all sure on.

Intel Core 2 Quad Q6600 Kentsfield 2.4GHz 2 x 4MB L2 Cache LGA 775 Quad-Core Processor - $194
or
Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor - $170
More cores? or more speed?

OCZ Reaper HPC 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory - $103
OCZ Special Ops 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1066 (PC3 8500) Dual Channel Kit Desktop Memory- $137
Do I care about DDR2 vs. DDR3?

VisionTek 900244 Radeon HD 4870 512MB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - $265
EVGA 896-P3-1260-AR GeForce GTX 260 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - $280
ASUS EAH4850/HTDI/512M Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - $158
EVGA 512-P3-N801-AR GeForce 8800 GT 512MB 256-bit GDDR3 PCI Express x16 HDCP Ready SLI Supported Video Card - $130
Choices choices! I'm sure I'd get by fine with one of the cheaper ones, but I'd really like my two-boxing to be smoothed as much as possible now and for the forseable future. The only other games I intend to play anytime soon are Starcraft 2 and Diablo 3, which neither I expect to have crazy requirements as per Blizzards record.

So the cost of everything after rebates ranges from $743 to $951, which is slightly over budget, but not by much. Beyond these hardware components I'll buy a cheap drive and will probably pick up a Windows Vista through school. The I/O stuff I'll steal from current computer.

Your thoughts and suggestions if you made it this far are greatly appreciated!

For multiboxing, more cores is usually always a better bet than more speed. Games are mostly single-threaded, so a single game will do better with a faster and lower-core-count CPU. However, we're playing multiple games, so multiple cores is usually better. Your OS and background tasks will eat up some CPU usage, so consider that 1 core. Each instance of WoW can utilize a core, so you're better off with the Q6600.

With that motherboard choice, you don't have a choice on RAM - it uses DDR2, which is not compatible with DDR3 (different physical slot even though the same pin count - it won't fit in the slot). Unless you really like the Wifi option, I'd personally go for the Asus P5Q-E P45 board (it supports up to 16GB DDR2 memory, instead of just 8GB DDR2).

Keep your old 74GB Raptor - it'll still have lower access times than a 7200rpm drive. I was using my 36GB Raptors in RAID0 for a long time while 5-boxing. You don't need multiple hard drives for WoW, just use multiple WoW directories with sym-links. Read the Wiki on that topic for the performance benefit of links instead of separate files.

The videocard is really up to you. A 24" monitor is a lot of pixels to push at 1920x1200, so a faster card with more video memory will help you more than someone with a 20". All the new cards are very fast for an old game like WoW, but for the future.. who knows? Faster is always better for future-proofing, unless you're open to the idea of upgrading the card later if you need to. The 4850 should do you fine for now.

WoW has very limited multi-threaded support. For two boxing, you will not see much of a performance gain between the dual core and quad core processors. There will be some, but real nice gains aren't seen until you are 4+ boxing. Just make sure you are assigning your threads to the different cores, properly.

At first glance, I'd say ADD MORE RAMz, but you already knew that. Up until today I have always recommended DDR2-800, because it's so much cheaper. But that DDR3-1066 you linked is a good deal. Will you notice performance gains between the two? Probably not, but it's a nominal upcharge for having something that is slightly better.

Judging by your current specs, I would take an educated guess that your current mobo couldn't handle a 64bit quad core processor and 8gb ram. Be careful choosing, check the manufacturers page for specific compatibility.

Your current vid card is on par with the rest of your system: three years old. If I had my choice of the 4 cards you listed; I'd take the GTX 260.

All yeh need to do is add more memory on yer current box and yeh would be able to 5 box it as long as yeh don't max out the settings.

it aint the hardware that needs tweaking its the software.