If your cable company choses to still provide analog cable signal you will be OK, and if they don't they will provide you with some kind of converter box.
If you don't have cable, then you can probably buy a broadcast converter box, but it would probably be half the price of a new TV.
The feds are going to subsidize at least a portion of the cost of the converter box.
Depends. You can get tube HDTV's that have the HD tuner built in. I got a referbed 32" tubr HDTV for $299 and it works like a charm.
Of course I assume that when they talk about DTV, they are actually talking HDTV as we know it now.