Hey, guys, let me first off say that this is my first time building my own computer. I don't have a huge amount of hardware experience, but I like to think of myself as fairly competent. 
I am a college student majoring in Computer Science, and I'm going to be mainly using this computer for gaming and programming. I don't need to be able to run Crysis at max or even ultra high, mainly because of my budget, but I'd like the highest value, obviously.
So my initial setup was going to look something like this:
Radeon HD 5850 1024MB - $300ish
either
Intel Core i5-750 @ 2.6Ghz - <$200
or
Intel Core i7-920 @ 2.8Ghz - $275ish
either
Asus P7P55D Motherboard - $150ish
or
Gigabyte P55-UD4P Motherboard - <$175
Crucial 4GB DDR3 1333 RAM - <$100
Samsung 750GB 7200 RPM SATA Hard Drive - <$75
(Some kind of) CPU Cooling Unit since I plan to overclock - <$75
Power Supply - ~$100
Case - <$100
Total WCS Cost: $1200
$ 300 General Expenses
Total Cost: ~$1500
Now, before you start formulating what would be best for me, hear me out. The main reason I chose the 5850 was not for its performance so much as my intention to (much later on so as not to include this in my expenditures) purchase an additional 5850 down the road and crossfire them. Like I said though, that is further down the road, so don't count that in the total cost of the machine.
The reason I am mentioning this right now is because, if I am correct, the dual 5850s crossfired together will not work with the P55 chipset that both of my chosen CPUs implement. Thus, I'm going to need a new (quality) CPU, which I think means I'm going to need a new motherboard as well.
If I have not made this clear yet, I've done plenty of research on video cards and am 95% sure that I want to stick with (eventual) dual 5850s. Unless you have something that is just a lot easier, cheaper, and better in terms of performance, leave that part alone.
The CPU and Motherboard are the main things I need configured. I plan to overclock my CPU, and because I heard that the i5-750 is a relatively cheap quad core that can be overclocked to perform as well as CPUs that are hundreds of dollars more expensive, I chose that one. You can pretty much rule out AMD, as I've already decided that Intel offers better performance.
Motherboards have somewhat been a mystery to me since I began dabbling in computer hardware. All I really know is that they allow everything else you purchase to communicate with each other, and that if you don't have the right motherboard, stuff screws up. 😀 So the quality of motherboard doesn't matter too much to me; let it suffice that I don't want to spend much more than 150 dollars on one, but I don't want it to hold my video cards or CPU back any.
I think I have to replace my RAM choice too, if I'm moving from P55 to X58. Crucial is a solid brand from what I've heard, and I would like to stick with them if at all possible.
Hard drive is low priority, as I'm not going to be using this PC for anything that would require loads of raw space, such as storing Blu-Ray movies. 1 TB of memory is PLENTY if not excessive for me; the main care in this category is access speed, and I'm not even willing to spend that much on drives since they're so cheap. $100 MAX.
And, honestly, after all this is figured out, can you tell me if this is even a good idea? I'm talking about the general concept behind this desktop: dual 5850s, your opinions on P55s and X58s, should I start from scratch?, etc.
Thanks so much, guys!

I am a college student majoring in Computer Science, and I'm going to be mainly using this computer for gaming and programming. I don't need to be able to run Crysis at max or even ultra high, mainly because of my budget, but I'd like the highest value, obviously.
So my initial setup was going to look something like this:
Radeon HD 5850 1024MB - $300ish
either
Intel Core i5-750 @ 2.6Ghz - <$200
or
Intel Core i7-920 @ 2.8Ghz - $275ish
either
Asus P7P55D Motherboard - $150ish
or
Gigabyte P55-UD4P Motherboard - <$175
Crucial 4GB DDR3 1333 RAM - <$100
Samsung 750GB 7200 RPM SATA Hard Drive - <$75
(Some kind of) CPU Cooling Unit since I plan to overclock - <$75
Power Supply - ~$100
Case - <$100
Total WCS Cost: $1200
$ 300 General Expenses
Total Cost: ~$1500
Now, before you start formulating what would be best for me, hear me out. The main reason I chose the 5850 was not for its performance so much as my intention to (much later on so as not to include this in my expenditures) purchase an additional 5850 down the road and crossfire them. Like I said though, that is further down the road, so don't count that in the total cost of the machine.
The reason I am mentioning this right now is because, if I am correct, the dual 5850s crossfired together will not work with the P55 chipset that both of my chosen CPUs implement. Thus, I'm going to need a new (quality) CPU, which I think means I'm going to need a new motherboard as well.
If I have not made this clear yet, I've done plenty of research on video cards and am 95% sure that I want to stick with (eventual) dual 5850s. Unless you have something that is just a lot easier, cheaper, and better in terms of performance, leave that part alone.
The CPU and Motherboard are the main things I need configured. I plan to overclock my CPU, and because I heard that the i5-750 is a relatively cheap quad core that can be overclocked to perform as well as CPUs that are hundreds of dollars more expensive, I chose that one. You can pretty much rule out AMD, as I've already decided that Intel offers better performance.
Motherboards have somewhat been a mystery to me since I began dabbling in computer hardware. All I really know is that they allow everything else you purchase to communicate with each other, and that if you don't have the right motherboard, stuff screws up. 😀 So the quality of motherboard doesn't matter too much to me; let it suffice that I don't want to spend much more than 150 dollars on one, but I don't want it to hold my video cards or CPU back any.
I think I have to replace my RAM choice too, if I'm moving from P55 to X58. Crucial is a solid brand from what I've heard, and I would like to stick with them if at all possible.
Hard drive is low priority, as I'm not going to be using this PC for anything that would require loads of raw space, such as storing Blu-Ray movies. 1 TB of memory is PLENTY if not excessive for me; the main care in this category is access speed, and I'm not even willing to spend that much on drives since they're so cheap. $100 MAX.
And, honestly, after all this is figured out, can you tell me if this is even a good idea? I'm talking about the general concept behind this desktop: dual 5850s, your opinions on P55s and X58s, should I start from scratch?, etc.
Thanks so much, guys!