As no-one has given a definitive answer (yet), I'll have a go at answering your first query - but only on the understanding that it may not be correct...
The Dell E228WFP is a computer monitor with a native resolution of 1680x1050 pixels, i.e. well up to the standards of high-definition video.
Provided your graphics card can run to it, the display will be top-notch via digital (DVI) sockets on the monitor and graphics card. This will include any HD video files downloaded onto your hard disc (720 or 1080).
But as far as I can tell, the monitor cannot display high-definition video /directly/ (e.g. broadcast, or from an HD/DVD player), so there's no need for an HDMI socket.
Anyone card to confirm or rubbish that deduction please?