I dont think it will fit. a PCIex16 slot i think is smaller than a PCIe2.0 or PCIe3.0. If it does fit it will only run at PCIex16 speed which will bottleneck that GPU.
NVidia GeForce 1GB VGA/DVI/HDMI PCI-Express x16 Video graphics Card+Low profile is available on newegg for 60 bucks. That looks like a pretty good card for what you are looking for.
I dont think you will be able to platy those games on your current system. Most newer game require at least 4 GB of RAM. The card I listed above will fit in your system give it a try.