Ram is good. Processor is okay. Graphics Card is sort've on the low end. Vista is bad. If you need to upgrade anything the graphics card and OS should be top priority.
Radeon 5670 ($70) would make a good upgrade, Could probably play dead island pretty good. http://www.newegg.com/Product/Product.aspx?Item=N82E16814127600 (http://www.newegg.com/Product/Product.aspx?Item=N82E16814127600)
Radeon 6770 ($110) would be the next best thing, Will play dead Island maxed out. http://www.newegg.com/Product/Product.aspx?Item=N82E16814125396 (http://www.newegg.com/Product/Product.aspx?Item=N82E16814125396)
GTX 460 768mb ($130), though the most expensive; would run pretty much anything you throw at it. http://www.newegg.com/Product/Product.aspx?Item=N82E16814162058 (http://www.newegg.com/Product/Product.aspx?Item=N82E16814162058)
how many watts is your power supply? you can probably check if you open the comp and look on the side, it might have a sticker on it or something.