All the networks are still broadcasting analog on the old VHF frequencies...it's another year or so before they get switched off permanently. I've never used an Apple Tuner card so I don't know how the software works, but in any case the RF block on the card will only be good for VHF (and low UHF). I assume that by changing the block (which you could pop out of a modern tuner card, or a $50 set top box or something...) that everything would still "just work"
edit: probably need to swap out a couple of other minor components too. I'll bet any Mac-friendly TV repair guy could take a look at the tuner card and tell you whether it's possible or not.