I think we've gotten ahead of ourselves here.
Does the OP have a reciever? And if so, which one?
If it can upscale, then there is no need to purchase a standalone DVD player when the xbox 360 can pass on the signal to the receiver just fine and let it upscale the image.
My suggestion would be this if he doesn't have a reciever that can:
+ Don't buy a seperate DVD player for a couple of reasons,
1st - You would be buying into a technology that is being phased out and is not compatible with new HD formats.
2nd - You can already play DVD's via Xbox 360.
+ Take that $200 you just saved from not investing in a DVD player and put it towards a Receiver. The reasons are simple. A good reciever will handle upscaling, provide HDMI switching etc.