really n00bish TV question

Basically my girlfriend's TV is one that does something I've seen in quite a few HD televisions recently. I don't really know anything about this other than it's making any film-shot material it displays appear as though it's been shot on digital and as such it looks horrible.

For example, we watched Friday Night With Jonathon Ross (a chat show) the other week and it looked fine up until they played a clip from the movie Run, Fatboy, Run which looked horrible and all as though the TV was trying to render the film-footage in digital.
I've seen this on other TVs and other people have commented on it, but my girlfriend is adament that there's absolutely nothing wrong with her TV's image quality and the rest of her family agree.

Please can anyone clue me up on this a bit more or give me some ways to demonstrate what I mean to her a bit better seeing as it's near-impossible to describe the visual difference between film and digital media when you could just show someone the difference. Are there any sites with comparisons for example? Or is there something on her television's settings that I could do to sort it out?

Sorry for how rambly this post is, but I don't really know where else to go for information. Thanks!

Really? Worst film you ever saw? Well, my next one will be better. Hello? Hello?