Is this a ok gaming computer?

That was a respectable machine 5 years ago. Now it's a little long in the tooth. Although a modern gaming machine doesn't need to be anywhere near as powerful as John imagines these days you want at least a dual core or preferably a quad core processor of a similar speed. You'd probably also want at least double the RAM, and again, at least 4GB would be better, and a faster graphics card. Looking at that system I'd suggest it probably isn't worth upgrading and a new base unit is the way to go. A machine that is several times better than this in all respects, and adequate for the games currently on the market can be had for under $400 if you shop around.