Help Choosing Graphics Card or maybe Mobo

If you replace that MoBo, you might as well say "build new".
I'm not a real guru, but I saw no one had responded to you.
I am running W7 Home on older Hardware than that, but I don't game. I'm running athlon 3500+. That is 64-bit, but single core and socket 939. My RAM is DDR 400. I have 4 Gig. of ram and that maxed out my mobo. n-force4 chipset.
I added a GT 220 this year, it is the fastest thing about my machine. My GT 220 has 1G. memory, I wouldn't consider one of those with 512 mb.
This GT 220 shows a windows experience 6.3 . My little processor is the slowest component on this scale, and I have it mildly o'c ed. that Windows experience thing is the only way I know to compare.
I don't know that game that you named, but I expect that GT 240 is all you need for the hardware that you now have.
BOTTOM LINE, only you know if you want add vid. card to what you have or start new. If you want to build new, I would go over to TomsHardware.com and look at some of the builds that they describe. Have fun!

gaming...and be something you could put into a new system if you buy another system in the next 6-12 months. Assume you'd bring the 850W PSU forward too.

By the way ... if you change the MB you might have to get a new OS unless the OS Win7 Ultimate came with the system.

VAPCMD