All of your hardware is pretty old. If you only have 80 bucks then maybe a cheap GPU upgrade but even with that I am not sure what you will be able to run. If you get to much of an upgrade on a GPU you may bottle neck or need more power for a power supply.
Well you can not get a 4870 except for ebay and one is going for 80 bucks. It would definitely increase your FPS. What brand is the PSU? its a decent deal and you can play minecraft for sure. As to playing wow dead island and Skyrim, well I dont think you will be maxing the graphics on most games with this upgrade.
I Would say if you can, Save up for a while and Build a new PC if you want to get the most out of your money. That would just be me though. There are some great 500 dollar builds out that if you can save that much.