There is a website called "System Requirements Lab" that will allow PC gamers to check out the most popular games, get their PC scanned for requirements qualifications.
The way it works is like this.
Start out Below by going to the following site:
http://www.systemrequirementslab.com/referrer/srtest
Next, pick a game in the list that you potentially want to purchase. Then click the "Can you run it?" button.
Note - Internet Explorer or Firefox may prompt you to install a component. If it asks you , say YES. The plugin installs and then it begins to scan your computers hardware components. Once its done, it will show you two categories. one category is the minimum required to run the game, and the other category is the "reccomended" category. You will see a graph, and either a Green " Pass " or red "Fail" if your computer meets the requirements for the game. And if you do not pass, it will reccomend to you parts that will allow your computer to run that game.
Its as simple as that, and it takes the guesswork out of bringing something home from your local Best Buy opening it, and then not being able to return something because you did not read the system requirements on the box. 
Happy Gaming!