Thanks for the help guys.
I got another file, and tried it, it played and is as good as DVD quality, but I'm not sure if it is true HD, still looked good though. I'm using a DVI output from my graphics card into the DVI input on the screen so it should be good quality. I'll do a search for "HR" and see what it brings up.
I still do not think it is worth all the extra money for HDTV from Sky yet as you only get a handful of channels and it is an extra £10 per month, plus £300 for a new box, I guess I will wait for that.
Jim - Luckily I don't watch 24 I only downloaded it as a tester, otherwise I would have to destroy you for spoiling the ending lol.