According to wikipedia : http://en.wikipedia.org/wiki/PCI_Express#PCI_Express_1....
PCIe 2.0 motherboard slots are fully backward compatible with PCIe v1.x cards. PCIe 2.0 cards are also generally backward compatible with PCIe 1.x motherboards, using the available bandwidth of PCI Express 1.1. Overall, graphic cards or motherboards designed for v2.0 will work with the other being v1.1 or v1.0.
Most of the time 2.1 cards aren't compatible right out of the box with a 1.0 slot.You will have to get a BIOS update to run a 2.1 card but the problem with that is that motherboard manufacture's stop posting updates for older model products.
Any PCIe card will work on any motherboard with a PCIe graphics card slot.
Your only issue would be possible CPU bottlenecking. Also, I'd get the GTX560.
- get a $20 to $40 CPU heatsink+Fan if you don't already have a non-stock one ( NCIX )
- *overclock your CPU (20% is probably stable with a good heatsink)
- run MEMTEST to test your RAM stability
*my older computer required me to first underclock my RAM before overclocking the CPU, because when I overclocked the CPU it also overclocked the RAM by the same amount.