Mr Cole
The Denon DVD-1920 is a 'Red Laser' player and like the majority of kit on the market will not be compatible with HD DVD (Toshiba) and Blu-ray DVD (Sony) discs when they arrive; these new technologies use a Blue Laser with a narrower light beam and will require a Blue laser equipped player.
You can add HDMI switches to your system if you require Inputs for addition HDMI equipped sources.
As Attu says your player is capable of up-converting Standard Definition DVD Video discs to an HD format - this is not the same as viewing a High Definition source.
You may want to consider the likes of the SnaZio SZ1350 - this DVD Video player offers you up-conversion on both Analogue 'Component' and Digital (DVI) video out and attached to a PC or MAC via a network cable can play back High Definition files you download onto your PC and also play back High Definition Windows Media Video files too.
See
Product feature : SnaZio Net DVD Cinema HD
Best regards
Joe