Just go to this site. Type in Diablo III on the search bar, or click Diablo III on the right side of the screen.
And let the site analyze your PC, I think it requires Java to run. You should have that already, hopefully.
It will tell you approximately if you can run it or not. It will list your PCs specs and it will list minimum/recommended specs for the game.
It's quick and easy, so you don't have to guess.
Also, if you want to see where your hardware stands go to cpubenchmark.net. It has a list of all high, mid and low ranged cpus, gpus and hard-drives.