A quad will give you a nice benchmark, but until there's a good selection of software that can take advantage of it, it won't mean much in the real world. I'd go with an E8400, which is very good for overclocking. The E8400 will smoke a Q6600 unless you're using software that's designed for a quad.
I like Western Digital. I have 5 of them, they run cool, and I've never had a problem with any of them. If you want a high speed drive, stick with Western Digital, but go with a Raptor. If you want speed and lots of space for media, I recommend a raptor as your main drive and a larger second drive for storage -- which you can always add later if you don't want the additional expense right now.
With a response time of 2ms, that monitor has got to be a TN panel, which means bad viewing angles and color. I had a Samsung 24" 245BW, which was a TN panel, and it was terrible. I replaced it with a Samsung 27" 275t, which uses an SPVA panel -- from what I've read, it's the same panel that the highly rated Dell 27" uses. It has a slightly higher response time, but I play HL2 and BF2 on it with no ghosting and the viewing angle/color is a heck of a lot better -- plus the larger screen size is a bonus.
I also second the recommendation of going with a monitor that supports 1920, but most monitors actually display 1920 x 1200 not 1920 x 1080.
If you're not familiar with different lcd panel types, do a google search and read up on it before buying a monitor. TN is the most affordable, but also considered the lowest quality.
I agree that DDR3 is nice, but pricey. The ram you've selected is about $350 on newegg, and you can get 4GB DDR2-800 for about $75. That's about $275 that could go towards a better monitor. The monitor will give you a more in your face increase in performance and it'll probably still be with you after you've replaced the ram/cpu/motherboard -- making it a good investment.
An option you may want to explore would be to get a motherboard that supports DDR2 and DDR3 so that you can have DDR2 now and replace it with DDR3 later when the price drops without replacing the motherboard. However, those boards usually have two slots for each type, which means a max of 4GB ram. How long it will take before you need more than 4GB ram depends on the length of time it takes for 64-bit to really become mainstream. Personally, I have 4 DDR2 slots, but either way, I think most people will get the itch to upgrade their systems again before 64-bit becomes mainstream.
Like a quad, you won't see much of a performance increase from a 64-bit OS until more software is available to take advantage of it. Meanwhile, it's a resource hog.
If you're wondering about DX10, Gabe Newell and John Carmack are less than impressed by it: X-bit labs - Valve Software to Stick with DirectX 9 for a While.
"They're really grasping at straws for reasons to upgrade the operating system. I suspect I could run XP for a great many more years without having a problem with it." -- John Carmack
Carmack questions games for Vista initiative // News // GamesIndustry.biz
Here's a demo of id software's tech 5 engine that uses 20GB of textures and doesn't use directx 10:
Watch the id Tech 5 WWDC demo, drown in its shininess - Joystiq
I guess the reoccuring theme here is that if there is software available, or will be in the near future, to take advantage of new technology, great, but if not, allocate your money to other areas where it will make more of a difference.
I like coolermaster btw. I'm about to pull the trigger on a Cosmos.