That's getting long in the tooth. But Leopard will mostly work. Some features require Intel processors. But you will benefit from most of Leopard's features. We don't know what that DVD playback spec means yet. I wouldn't worry about it.
Oh yeah I agree with Kodex & Peace you should put in two 1GB sticks to max out the ram. 512MB of ram is fairly pathetic. Hope if you just bought it you didn't pay very much for it.