The 768x576 is the resolution the TV is receiving which in this case is standard PAL, you TV will have scaled the signal to match the screen which it will with any signal.
Even though you have the DVD connected via HDMI its only going to send a standard PAL image unless you tell it to upscale the image (providing the DVD can upscale) you may find though that the TV does a better job of up scaling the image than the DVD player.
If the DVD sends the TV a standard PAL signal the TV will display it as 768x576 even though the TV is up scaling it to fit the screen, if the DVD up scales the image the TV will display the image as what ever the DVD player is sending to it but in reality you may be looking at the same picture.
Thats the problem with up scaling DVD players, the TV's upscale anyway and in some cases better than some DVD players can do it.
