Welcome to the forum!
First off, the Phenom is a 64bit processor, you just may have paired it with a 32bit OS. But yeah, its dog slow compared to the new stuff out now for HD video editing.
Second, How soon are you looking to build? I only ask this because you are literally 3 weeks away from Intel's next i5/i7 series chip; the Ivy Bridge. It looks quite promising, about 5-15% boost in most apps compared to the current i5/i7's for the same price point. Although, Intel did say that availability on launch could be limited quantities as they try to allow OEM makers first to sell off their SB chip inventory, but this is mostly towards the low voltage, mobile markets.
Not only that, but Nvidia is releasing their next gen Kepler series gpu's next month; nothing you should actually worry about, except that it could lead to price cuts for their current 500 series line up; specially when AMD's mid range 7800 series hits the market today or the fact that AMD gpu department has been doing pretty well across the board. But, I'd say stay with the nvidia CUDA platform since that is what Adobe Premiere currently uses for CS 5.x; CS 6 could change that when/if they added support for OpenCL for the AMD guys, but even then, nvidia cards actually run OpenCL apps better. Although AMD has said they redesigned the way that the 7k gpu's handle OpenCL apps better. Only time will tell, but safe to keep it with nvidia.
If you can't wait, then you still get a blazing fast machine that will eat through HD material alive. Your list is pretty much on par except for one thing: You can't use triple memory kits in a dual channel configuration. You have to install in pairs or even numbers to get the dual channel memory bandwidth boost with sandy bridge's.
i7 2600k Sandy Bridge build:
With this, I'm assuming you will be recycling the case and power supply. This will net you a pretty decent setup for HD video editing if you can't wait for Ivy Bridge. CPU/Mobo
Like I said 2 or 3 times already, Ivy Bridge, Ivy Bridge, Ivy Bridge! Less than 4 weeks away! But the i7 2600k will hold it's own. I paired the cpu with the Cooler Master 212 EVO cpu cooler that will net you quiet a bit of overclocking potential; probably hit 4.5-4.8Ghz with ease and still be quiet cool. Memory
Also side with those choices is the AsRock Fatal1ty p67 motherboard. Why did I pick this? because its on sale for half off and a fantastic board over what I'd usually suggest around $30-40 more. It's the very few boards still that has the old IDE/PATA connectors in case you are still rocking some old drives. The board has tons of other options like 10 SATA ports (6x SATA3; 4x SATA2), 4x USB 3.0 slots along with the 20pin internal connector and three 16x pcie 2.0 slots. You don't need all of the pcie slots, but its nice to know that you can add a x16 slot raid card and/or a pcie SSD... if/when you get bank.
And since I added a proper sized SSD to the budget, don't need to get Z68 for the SRT SSD caching feature. This board is a great buy.
Here is where I maxed out, because you can really use up some ram with what you are doing. 32GB of RAM may seem crazy and expensive, but let me tell you, you will love it when you do high res photoshop work or HD video editing. Specially with Premiere being a hog with system memory. And since you only have 4 slots, we had to use the expensive 8GB modules to max our the board. You still come out on top, being under your $1500 price point.SSD/Hard drive
If you want to be sensible, you could get away with 16GB (4x4gb) kits; Just try to keep it at cas9 or less, 1.5v or less, 1600 speed ram. No need in wasting your money on high speed ram like 2133 since most of the time, those modules are running at slower timings and negate any speed boost in bandwidth from it. Plus most of the time, they are no more than overclocked 1600 modules anyhow for double/triple the price tag. Even the good 2133 speed modules will only net you a 1-7% increase in performance; hard to justify the performance for such high costs.
You'll notice that I picked out an SSD for your system because of two reasons: 1. It'll boost your load times with the OS and apps and 2. SSD's make great scratch drives for your projects.Video card
I picked the Crucial M4 128GB because its a great performer with compressed files like HD videos, mp3's and jpegs as well as being rock solid and reliable. It's also not a bad price at $156 since it tends to be around the $170-180 mark. There are other SSD's on the market, but you should stick with the more expensive ones that use sync NAND's (like the M4) that perform way better with compressed/encoded files like most media/videos are.
Paired with the SSD (obviously since its kinda small) is the 3TB seagate drives for a decent price; its not much more than the 2TB disk you selected above. Should provide you with ample storage for your HD videos, but I'd maybe look at picking up a 2nd drive and atleast do raid mirroring for data security. You can probably drop it to 2TB so you could afford two.
And to make myself clear, you still need to backup your data/important docs with offline media, whether it be an external hard drive, tape, dvd, cd, or blu-ray; nothing beats a proper, regularly timed backup solution. Even have it offsite somewhere in a safe or a friends house; shit does happen.
You don't need to do crazy multi-card solutions for gpu acceleration support with CS 5.x; actually you don't even need to spend $150 on a card for this. You can literally get away with a cheap $30 GT 430 card for your basic gpu acceleration with the mercury playback engine. You'll lose a bit of horsepower when you want to do live previews with lots of filters, but if you are doing normal cuts and such, you can cheap out here. Even then, you can always have your i7 do pre-renders in no time flat.Optical
now CUDA does offer some post processing abilities with their encoding through premier, but its kinda flaky at best since it only supports a certain number of filters and effects. Plus its even worse when you want to do a final export of your project and want gpu acceleration since AME doesn't support this so you can't do batch adds. Plus its also skiddish if you run multiple monitors and move premier export tab around. Donno whats up with that.
Same Asus Blu-ray burner drive as you listed, but its not listed as $70 on NCIX...Operating system
Win7 pro 64 bit... nuff said. Lets you take advantage of more than 16GB of ram that's limited on the home edition.
That pretty much wraps it up. Everything should fit in your current Antec 300 case just fine and your current 650w psu should be more than enough to hand this system. Even with you overclocking, you might be pushing 400-450w max on load.