From the Durango thread:
Here's what I put together after a bit of messing around:
GPU: ASUS GeForce GTX 660 OC DirectCU 1020MHZ 2GB 6.0GHZ GDDR5 $199.99 after rebate
CPU: AMD Athlon II X4 640 $76.98
Mobo: ASUS M5A78L-M LX Plus mATX AM3+ DDR3 AMD 760G $54.99
RAM: Corsair CMZ8GX3M2A1600C9B Vengeance Blue 8GB 2X4GB DDR3-1600 $49.99
PSU: Thermaltake TR2 600W Power Supply $39.99 after rebate
HD: Seagate Barracuda ST31000524AS 7200.12 1TB SATA 32MB Cache $67.99
Case: Zalman Z9 Plus ATX Mid Tower Case Black, several case fans included $34.99 after rebate
Mouse/Keyboard: Logitech MK120 Desktop Keyboard and Mouse Combo USB $14.99
Blu-Ray Drive: LITE-ON Black 4X BD-ROM 8X DVD-ROM 32X CD-ROM SATA Internal 4X Blu-ray Reader $25.99
Webcam: HP HD-3110 Autofocus 720p 30FPS Widescreen Webcam $11.99
OS: Linux trololol (psst.. you can still run Windows like everyone else does, I won't tell anyone) $0.00
Total: $577.89
This is over the budget of $500, but it's a good system for the price. The CPU and GPU are very overclock friendly, and the PSU can handle it.
Downgrading to 4GB DDR3 RAM and a 500GB HD is about $45 cheaper, and getting rid of the blu-ray drive and webcam is $38 cheaper. The "cheaper" total is $494.91, under $500 for the same gaming performance provided the 4GB DDR3 doesn't come back to haunt you.
For an AMD GPU I'd look at trying to get a 7870 on sale for around $210-230.
Sorry to be stunningly naïve, but when people buy Linux-installed systems, and want to get Windows, from where are they buying their Windows OS? Is there some cheap deal, such as OEM versions of Windows on the cheap? Or are they pirating the OS and, if so, how are they getting around the security measures of Windows Update, which theoretically checks with the mothership for validity before updating?
Also, if I have older PC which shipped with Windows, can I transfer those licenses to a new machine, or am I SOL?
You're in Japan, right? MS used to have digital-purchase-and-download of Windows 7 from its store site; now it's just Windows 8. You can actually download ISOs of almost any version of Windows XP or 7 from their digital distribution partner (Digital River; do some searching on Google), but you need a valid key to activate the OS once installed.
If you can get Newegg (or a friend in the US) to ship to you, they might be the best choice for the easiest purchase. $140 for Windows 7 Professional.
As far as using the OEM product key that was on one of your old computers, I've heard that some installs check for a BIOS key to confirm that Windows is being installed on a computer from the same OEM. You may need to do some hacking.
OEM CD/DVD are different from retail CD/DVD; keys for one won't work with the other. You can edit a file in the ISO to change that - google it.
If you can, slipstream SP3 (for XP) or SP1 (for W7) into your install CD/DVD using nLite to save time after you install the OS. Much faster to incorporate the service packs into the installation media than wait for it to download. W7 may no longer allow you to slipstream, now that I think about it.
Not all MSDNAA/Dreamspark participant campuses have the option of getting free W7/8; some (like mine) require you to be a computer science major with special credentials before you can access that stuff. Otherwise, you have access only to developer tools (Visual Studio; Server 2008, etc...)