Here's the problem: You have an older Windows PC (or maybe a brand new one with some limitations, like a netbook) and you want to know if it can run game X, but you don't want to search out the system requirements for game X and try to figure out if your system matches that. "Minimum Nvidia GeForce 2 or equivalent? How does that compare to my built in Intel 500 ?" you might say.
Here is a solution: http://cyri.systemrequirementslab.com/CYRI/
Just go to that website, choose the game you are trying to find from the list (or search for it) then click the "Can You Run It?" button.
The first time you run this you will have to install an active X control (click the yellow bar that appears at the top of the browser.)
It will analyze your hardware and give you a report of whether the game will run, or what part needs to be upgraded to play.