Don't build it over time, save all up the money until you think you want to buy it.
As it stands right now, you can spend about ~1000-1300 for most games that are out right now you'd play on high to medium high. It really depends on if you go with AMD or Intel. Intel is much better, and will last longer as it's technology stays relievent much longer. AMD is more budget side and aimed towards the small man. The man with shorter pockets. Hopefully with Bulldozer, they'll actually start to become a better brand and be less "Budget." AMD also owns ATI now and has rebranded as such if you didn't know and unless you can afford a single GTX 580 stick with the 6950/6970. 6970 is just behind the GTX 580 but ahead of the GTX 570 about 95% of the time.
Yes you can build it for cheaper than I'll show you on the bottom. But honestly I'd wait till 1)Bulldozer comes out 2)BF3 comes out. Or at least the beta comes out. 3)AMD and Nvidia(I believe) are releasing the next family of GPUS by the end of the year?
Do you need mouse and keyboard?
You could save some money by dropping down to a 6950 and an i5 2500k, maybe a cheaper motherboard. You could drop down to 8GB (2x4GB) instead of the 16 I gave you

I like having more than I need. Makes me feel better and eases my mind (No matter what Phobus says about 4GB being the max you need

). APB will make you almost max out the 4GB not giving you a lot of room. Haven't ran into a game that get's past 85% under extreme cases but APB pushed mine to 98-99% most of the time.. :/
Keep Win7 Pro 64-Bit. Home Premium 64-Bit can only recognize 16GB worth of memory. That's RAM and graphical memory. Pro/Enterprise/Ultimate 64-Bit reads up to 192GB. Why does that matter? With that setup I have you with 16GB of RAM and 2GB on the graphics. 8GB of RAM is all you really need right now. I haven't ran past 50% usually unless I play GTAIV then I can actually hit in the high 60's.. Or when I have photoshop, skype, BFBC2(Or any other game really), Pandora radio, steam, xfire a few others running at once. Hahaha.
Quote from the build guide Phobus has written in the forums.
Phobus: So why do I only recommend 4GB of memory? First I think I should explain 32-bit and 64-bit programs and operating systems. A 32-bit piece of software can address up to 2^32 bits, which is 4GB(GiB, if you want to get technical) of memory. So let's say that you have 4GB of memory, with a 1GB video card. The operating system can only handle 4GB of the 5GB+ (some things on the motherboard may need to address memory) you have available. Now 64-bit software can address up to 2^64 bits, which is something like 16YB(Yhottabytes, which is roughly 16,000TB) of memory. So you can use up all of your memory that you have available.
Although he says "So you can use up all of your memory that you ahve available, Microsoft does limit each version of Windows of how much it can read.
This is the setup. More or less what I want.
