The 300D does not record video, the LCD panel on the back does not display a real-time view of what you're about to take, and there's no electronic viewfinder in the eyepiece. That said, when looking through the eyepiece, you're seeing in full resolution what the CMOS sensor will see when the mirror flips out of the way. There's no video because there is a mirror in the way and also because of the way image data is transferred off the sensor -- it's just not possible.
marius