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I believe the GA-7NF-RZ is an AGP MOBO so the newer PCIe GPUs will not work. To verify the type 'AGP' download CPUz and look at the Mainboard tab. CPUz -> http://www.cpuid.com/softwares/cpu-z.html
If it states "Graphics Interface AGP" then I'm correct.
AGP GPUs -> http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007709%20600007850&IsNodeId=1&bop=And&Order=REVIEWS&PageSize=20
I would not spend a lot of money and the AGP will not perform very well in current games. You are approaching a time where it's time to consider a new build/PC. The EVGA 256-A8-N401-LR GeForce 6200 seems to be good.