BSOD BSTD :
yes it will run, provided your PSU can handle it, as I said before, the 960 is a low power card, esp. considering its capabilities. just make sure you can fit it into your case.
You should also get a new mboard as soon as you can. That mboard only supports PCIe 1, gtx960 is pcie 2.0 but will work in the 1.0 slot, however this means a slower data transfer rate = you wont be getting the most out of the card.
Same goes for the RAM, that mboard supports DDR2 RAM, you'll get better performance with DDR3.
So definitely buy the GPU, but I would also buy a new mboard and new RAM when you get the chance, you will really notice the difference then. That Mboard will throttle the 960 a bit unfortunately.
I already have a LGA 2011-V3 system, so DDR4, i7-5930k, Samsung 850 EVO, 2x Gigabyte 970 G1 in SLI.
My old computer though, needs an upgrade, I have it since 2007, but now it's collecting dust, so I was thinking of reusing it as HTPC without spending a big amount of cash, and the GPU upgrade made a lot of sense. I don't need to make the most out of the GPU, I'll be watching 1080p content at most.