[NooB] questions about HD - Newly purchased

I recently bought my first HDTV (Hitachi Ultra Vision 51" Projection).

I have it hooked up through component cables and I get HD through my cable box and it looks great on HD channels, but I was wondering about the blocked off sections on non HD channels. There's dark grey boxes on the left and right sides shrinking the picture down to a box. I understand this is normal? Can someone explain why?

Also does that hurt the tv at all? Or, is there any way to stretch the non HD channels to the rest of the screen?

Also, any comments on that particular brand/model?

TIA