A few things you need to consider with lcd tv's
They need to be bedded in(i left mine on for nearly24 hrs).
The closer you sit the worse the pic actually gets.
The picture is bloody terrible straight out of the box,they need to be set up.
A sd tv signal will not look to clever on a hd tv,some tvs look better than others.
Not all tv channels transmit signals at the same quality(watching footy on setanta is crap).
Idmi cables,dont buy a expensive one i have a £60 lead and a £6 lead and there is no difference to be seen.
A few links that might be helpful for you
AVForums Home
Home Cinema Forums Forums for Home Cinema Enthusiasts
Do a search for your model and have a read up on them.
I have a 47" toshiba and have no trouble with blockyness.