Hello McGirk242,
I truly appreciate your smart move with not needing a DVD drive, i have been not using a DVD drive for more than 1 year, and i never needed, i know good tutorial on how to install Windows 7 from USB drives, and with the use of Imdisk(something like Daemon Tools) you wont need DVD drives for ever.
Also from what i know in linux using Unetbootin you can probably install most of Linux Distro`s
Linux does not benefit much from directx, but more from OpenGL, and i reckon AMD cards are more mature in OpenGL than Nvidia.
And AMD HD graphic drivers have come along way, and i have an APU and i used it with Lubuntu, and i simply installed a package called:
fglrx, also installed the latest drivers from AMD website manually is fairly simple and easy and comes with the great GUI program that i reckon provides more tinkering option that others, simply head to AMD driver website :
http://support.amd.com/us/gpudownload/Pages/index.aspx
Select your card, and after downloading the tar package, you will need to extract it, then close the xserver session, i reckon if i remeber
correctly it was by /etc/init.d/gdm stop, then head to tty1 and login and execute the install script, and then its was done and it was faily easy
in my opinon.
Going back to your question:
You have 400USD which is not much but we have to work out something, i reckon you also need a monitor and PSU unit correct?
IF so we will need a cheap quad core + AMD 7750 (make sure its GDDR5 and DDR3) which will be great combination:
Please read here, to find out my source of this recommendation :
http://www.anandtech.com/show/6934/choosing-a-gaming-cpu-single-multigpu-at-1440p/9
If I were gaming today on a single GPU, the A8-5600K (or non-K equivalent) would strike me as a price competitive choice
for frame rates
and due to there is and FM2 mobo socket that are cheap that maybe a way to go:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819113281 = 109 USD quad core CPU
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131481 = 90 USD great GPU (you can grab the 7770 but with your budget were abit limited)
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136770 = 60 USD (normal no frill 500 GB HDD)
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131885 = 55 USD (mobo its abit of no frill with no Usb 3.0)
http://www.newegg.com/Product/Product.aspx?Item=N82E16820239263 = 30 USD Ram 4 GB DDR3 1 slot, in the future you can purchase another one
http://www.newegg.com/Product/Product.aspx?Item=N82E16811233073 = 25 USD any other cheap case will do
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139026 = 45 USD good PSU + certified.
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total : 414 USD ..... shit
still without a monitor , maybe then you can forget about the GPU and use the AMD integrated GPU for some time, do a research on it itca
called HD 7560D and after while when you have money or when the AMD hd 8000 gets released you can purchase a GPU or the
same 7750.
Hope others can help, also please report back if there is any components that you can re-use like HDD drive or montior or something.
Of course there is alot of alternative setups out there, but i reckon this is the best balanced setup for your money, and its also power
efficent and quiet (upon adding and external Graphic card, the the AMD APU will stop its internal Graphic card, and thus be more quieter
and power effient.)