You will need to find out what version PCIe it is. I couldn't find which version that mobo uses.
GTX 900 series use PCIe 3.0 specification. There is some degree of backwards compatibility but will result in reduced speed and may require BIOS updating.
How old is it? My MoBo is from early 2011 and came PCIe 3.0 ready. Anything older than that is likely PCIe 2.0 or lower.
Edit: I have found that Newegg reviews for your MoBo date back to 2006 so that probably explains why I couldn't find the PCIe version info on the ASUS page... It is likely 1.0a or 1.1 which means a 9XX card should work with BIOS update but will use only around 25% of the bandwidth for which the card is capable of.
Gigabyte P67A-UD4-B3, Intel Core i7 2600K, 16GB Corsair DDR3, EVGA GTX 970 SC, Win7 Pro 64-bit SP1, Primary monitor @ 1920x1080, secondary monitor @ 1024x1280
