DirectX 12 isn't a thing yet, but I think you are talking about DX 11.1 which was reported to be exclusive to Windows 8. However Microsoft jumped back and said it will be coming to Windows 7. http://www.tomshardware.com/news/Service-Pack-1-Windows-7-DirectX-11.1-Runtime-Chuck-Walbourn,19135.html
I recommend posting up your build specs to this sub-reddit: http://www.reddit.com/r/buildapc There are tons of computer nerds on there who will look over your specs and give you recommendations on price and performance. Also, with 1500, you should be able to build a pretty awesome machine. About Windows 8, I heard…
You can basically get whatever you want then with $1500 to spend on the tower alone lol. 3rd generation Intel i7, 16-32gb of ram, and an nvidia 670 or 680. You might be able to squeeze in a solid state HDD which make everything load super fast. My only major recommendation would be to get Windows 7 instead of 8 because the…