latley, ive noticed that there are topics that relate to either "can i run grand theft auto 4?" or, "can i run <insert gamename here>?".
well, about five years ago, an online app was made by the name of "Can I Run It?" to help people that have that sort of question.
what the app does is that it scans your computers non-personal information; chipsets, drivers, and everything else hardware related, and determines how well you can play the game you selected.
while it may not answer all of your questions, its sure to be of at least a little help :)results example(http://img72.imageshack.us/img72/6121/67630415.jpg)
quick and easy.
enjoy :)