Will this video card work in my computer?

Hi all, I am looking to upgrade my video card because the current GeForce 210
is really choppy and doesn't play .mts and .m2ts files, which are hi def videos. I upgraded to the GeForce 210 as the onboard graphics NVIDIA Geforce 6150 SE would not play them hardly at all. My system is an HP Pavilion a6614f PC running Vista Home Premium. The motherboard is from Pegatron Narra3 and Manufacturer's motherboard name is: PAsus M2N68-LA. Specifications page is here: http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01....

The motherboard has one PCI Express x16 slot. The video card that I would like to put in is: SAPPHIRE 100289VGAL Radeon HD 5670 1GB DDR3 PCI Express 2.1 x16 HDCP Ready Video Card. The power supply rating is 300 watts and apparently (hopefully) the Radeon HD 5670 is not so power hungry that I will have to upgrade the power supply. Since the motherboard specs do not state if it will accept PCI Express 2.0 x16 or PCI Express 2.1 x16, I'm not sure if this card will work because it may not be backward compatible with the plain Jane PCI Express x16 slot. Therefore I may be wasting my money on a nice card that will not work in my machine. The specs. on the card are here: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Thanks in advance for your help.