System requirements for games can be downright confusing for the non-technical user. Now, admittedly, most gamers will have a fair understanding of the hardware in their computer, and where it ranks relative to other systems, but for the few that don't, there's a great tool put together by Husdawg at systemrequirementslab.com. Simply select the game you want to check, and then the java detect link, and it will check the hardware in your computer, and tell you whether your system will run the game.
http://www.systemrequirementslab.com/CYRI/
Game coverage is quite good, although I've found a few older games (meaning from a decade ago) that aren't listed. Considering that an entry level computer from a few years ago will usually play one of these games at the highest settings without any problem though, I don't think that's a problem.