you will have to buy a new tdt box which will take the card
not necessarily.
many of the new flatscreen TVs have a PCMI slot that can accept a card reader, which can be used to read the TDT Premium (thats what the Pay TDT system is being called!) when they are made available.
similarly, you will need a new TDT set top box for HD, as some channels are currently testing HD channels also, and many HD TVs with TDT built in do not actually have a TDT HD tuner built in, just a plain Standard SD tuner.
Only two channels have so far been confirmed for TDT Premium, GOLTV and AXN.
GOLTV is on a promtions stage at the moment and will be free until the 31st August. Then you will have to pay for it. However, as it is free, they cannot show many football games (champions league for example) as other spansih broadcsaters have the free to air rights to them. Although last weekend they did have 4 UK Premiership matches - no english commentary though.