Hi I am in the UK and have NTL digital tv (crap i know ! I've no outdoor aerial)

I have an old Avertv tuner card about 4-5 years old. I have connected the digibox to the tuner card by a scart adapter to composite lead. The picture isn't too bad on the pc but not that crisp (19" widescreen TFT)

1) Would it be better to connect via co-ax?
2) If I were to buy a newer tv card has the technology improved over the last few years??

I would be greatful for any suggestions.