parkisg

I am wondering, since I am going to be getting a tv soon, and I was thinking of getting a HDTV tv, and I understand that in order to receive this you need to receive hdtv service to get it to work.

But my question is about if you dont have HDTV service and your running standard cable through a HDTV, will it look like a regular tv picture that didnt have the HDTV service.

Now I ask this question, I am new to this area about newer tv's.

What I am really wondering is that I was out shopping looking at tv's around 500 to 700 dollars and trying to choose if I want the HDTV, and if the picture is going to be messed up if I dont order the service for the HDTV.
Now what brought me to this question is that I went into a store and seen a 30" flat panel tv with the broadcast network "TNT" running through it(not sure if its cable or whatever). The thing that struck me was that the movie Kill Bill was on and I noticed the picture looked really really bad, worse than standard quality tv(and this is a flat panel tv with HDTV) , but when it went to commercial - the picture quality looked good(with no problems), but the movie came back on and still the quality of the picture was horrible. It looked pixilated.
Now after seeing this I asked the clerk and he said that some things come in really bad, he said especially like car racing.
Next I went to another store and some really young clerk told me that there is an analogue mode that you can switch to on HDTV tv sets, and he said it switch's it back to standard tv, so at least you can watch the movie in standard quality, instead of that horrible picture I discribed above.
Now, was he right?, is there an Analog mode to switch your tv to in cases like this, and is it easy to do.
Also, if there is such a thing(andalog mode) to correct the problem I stated, is it a option you can have on all HDTV sets?