How much should I expect to pay for a case with good cable management?
About the same. NZXT's Gamma(shown), Beta EVO, and M59 are all either around the same price or cheaper than the Two Hundred. (the M59 is an upgraded Gamma) I would spend a bit more and get a really nice one, though...these are all budget cases, if very good ones. Cooler Master's HAF 912, 690 II, and Storm scout are all very good buys. The 912 is $60 on Newegg.ca, so it's an awesome deal right now. Put a bit more into it, say ~$130, and you can get a really nice full tower case.
In general what you want to look for in a good case are (1)a bottom mounted PSU, (2)sideways mounted hard drives(cables face the right side panel), and (3)holes in the motherboard tray to route cables through. Most important on that last one is (4)a hole right next to the PSU to put the cables in initially. A hole(5) to mount a CPU cooler bracket also helps, as well as (6) tie down points. Some cases have even more features, but these are the basics that a good case should have.
This thread should give you a good idea of what that's all used for:
http://www.computerforum.com/164335-post-your-cable-management.html
What do you suggest for the motherboard?
Without knowing your options I can't tell you, but you should be able to find something of similar quality for cheaper. Just make sure it's a Gigabyte or Asus (I prefer Giga), and is new enough to have SATA 6GB/s and USB 3.0. If you want a particularly nice board, look for one with the 890GX chipset. One with 890FX is even better but they're a lot more expensive and probably a little unnecessary for your build.
If I get 8gb of ram, does mean I need a 64bit version of windows 7? I've heard that the 32bit only supports up to 4gb of ram.
32 bit will actually only use something like 3.25 gigs of RAM. There's really no point in not going 64 bit nowadays. There were some compatibility issues when XP 64-bit came out, but that's largely a thing of the past.
For the CPU, does any software support 6-core cpu's?
All of that editing software should, yes.
As far as GPU, I know nothing about them, I want support for HD video. Throw your suggestions. Should I be doing Crossfire?
Honestly, even though it won't be as fast as a GPU, the CPU won't exactly be "slow" at rendering videos in Premiere, so I'd just get a good mid-range GPU to use with Photoshop and hardware-decoding your movies. This will save you money both now, and later on when you pay the power bill.
The GTX 460 is a good mid-high unit, though the GTS 450 would suffice if you don't want to pay for the 460. If you want to play games, though, get the 460...it'll be worth it. On the ATI side, the 6850 and 6870 are their newest cards and would work just fine, though Nvidia is typically better for this sort of thing.
Crossfire (SLI for nvidia) is usually only useful for upgrading a gaming system, since two cards in crossfire are usually more expensive than a single card that's just as powerful. However, once your current card ages a bit and comes down in price, it's cheaper to throw a second one in than it is to upgrade. Neither are supported by CS5 anyway.
I don't want to buy parts online.
That's going to limit what's available to you, somewhat. Where are you buying from?
I'd consider Newegg for at least some of your parts, though...they have great customer service.
